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.