Hypocrisy is the contrivance of a false appearance of virtue or goodness, while concealing real character or inclinations, especially with respect to religious and moral beliefs; hence, in a general sense, hypocrisy may involve dissimulation, pretense, or a sham. Hypocrisy is the practice of engaging in the same behavior or activity for which one criticizes another. In moral psychology, it is the failure to follow one's own expressed moral rules and principles.
Cursing the wrong doers has come in Quran in 39 verse. Muslim must disassociate from hypocrites and wrongdoers whom Allah (SWT) has cursed in Quran. You can read these Quranic verses to see the great importance of cursing the wrong doers:
Sura al-Baqara, verse 88 and 159.
Sura Annisaa, verse 47 and 52.
Sura Tawba, verse 68.
Sura al-Ahzab, verse 57 and 68.
'Sura Muhammad, verse 23.
Sura al-Fat-h , verse 6.
Sura al-Ankabout , verse 25.
Obviously, we should avoid cursing the religious figures of other communities in front of their followers as Allah (SWT) says in Quran : Do not verbally attack what is been worshipped by the disbelievers, so that they shouldn't attack Allah with out knowledge. Sura 6, verse 108.
Additionally, Qur'an 47:30 says that the hypocrites could be recognized by their tone of speech (either their tone of voice, or the tone of their choice of words).
It is related on the exegesis of this verse that the Companions Abu Sa'id al-Khudri and Jabir ibn 'Abdallah al-Ansari said: 'Their tone of speech meant that they hated 'Ali ibn Abi Talib, and thereby we knew who the hypocrites were in the time of Allah's Messenger.'
Of course, the verse does not specify dislike of Imam 'Ali, but Imam 'Ali was known to be the sort of person that only a hypocrite or nefarious person would dislike.
In any case, 'tone of speech' can also be take in general to refer to other signs of hypocrisy in what they said.
The criterion for recognising the hypocrites is their negative attitude towards Ameerul Mo'mineen Ali (AS). Virtuous companions have heard from the Prophet Muhammad (SAWA) that no one likes Ali but a believer, and no one dislikes Ali but a Munafiq (hypocrite). This authentic Hadeeth is narrated in Saheeh Muslim (number 113) and Musnad Ahmad ibn Hanbal and Tirmithi and Ibn Maajah and many books of Hadeeth.
Simple search in Sunni books of Hadeeth leads to the fact that all the three whom you named ran away from the Jihad.
1. Abu Bakr:
Al-Haakim Al-Nisaboori who is one of the well known Sunni scholars narrated in his famous book Al-Mustadrak Alal Saheehayn, Volume 3, Page 37 that Abu Bakr ran away.
In Saheeh Bukhari and Dalaa'l Al-Sidq , V. 1, P.362 and Noor Al-Absaar by Shiblanji, P. 87, you find that Umar ran away.
Ibn Katheer (student of Ibn Yatmiyyah) mentioned in his books Al-Bidayah Wal Nihayah V.4, P. 28 that Uthman ran away.
Many other Muslims have also run away from the battles due to weakness in the faith. Only the firm and strong in faith stood fast and never ran away.
Exposing the hypocrites was declared in Quran by their deeds but not by their names. Same was done by the Prophet (SAWA) who did not expose their names.
The Prophet (SAWA) has clearly stated that many of his companions will change and turn back from right path after him then will be sent to hellfire. (Saheeh Bukhari, Hadeeth number 4259
and Saheeh Bukhari, Hadeeth number 6098,
and Saheeh Bukhari , Hadeeth number 6099,
and Saheeh Bukhari, Hadeeth number 6026,
and Saheeh Bukhari, Hadeeth number 6528.
The hypocrites were in many places including Madina. The hypocrites were from different tribes and places including Makkah and Madina. Hypocrites used to join hands with enemies of Islam including Jewish enemies and Mushriks of Quraish and others.
The state of every human being depends on his or her intentions and deeds. Those who believe and accepts the orders and guidance from Allah (SWT) will enjoy peaceful heart and pleasant life here and hereafter. Those who reject and insist on rejecting the Truth, cause themselves to be away from Allah with dark hearts and closed minds.
The seal on the hears of hypocrites is nothing but a result of their bad intentions and bad deeds, and it will remain as far as they remain rejecting the Truth, but if they change themselves to better, Allah (SWT) will change their situation and the seal will not remain. (Allah will not change the situation of people unless and until they change themselves. (Sura 13, verse 11)حتى يغيروا ما بأنفسهم
Allah (SWT) kept the gate of accepting the repentance open for every one till before the moment of death. Those who spent long life in evil but repented and sincerely asked for forgiveness, will be forgiven as Allah (SWT) has promised (O my servants who transgressed against themselves (by committing evil deeds), don't despair from the mercy of Allah, verily Allah forgives all the sins)(Sura 39, Verse 53).
As soon as the bed person whose heart was sealed, changes his life to a better one, his situation will be changed and the seal will not remain.
As Allah (swt) knows the future, He also knows that even if the door of guidance is open, the hypocrites will never choose it. His setting the seal upon their hearts is not an emotional act, but rather a logical response to the action of the person. That said, the Qur'an does not say that the seal is permanent.