Will Allah forgive sins committed during a period of deviation from acts of obedience after repentance, and will previous sins return if one relapses after repentance?

Whoever repents from a sin and then returns to it is only held accountable for the sin he returned to, and the sin he repented from does not revert to him. Abandoning prayer is a great sin, greater than adultery, theft, drinking alcohol, and killing a soul. It is obligatory to offer sincere repentance from all sins, and whenever you sin, you must repent and not despair, for "the one who repents from a sin is like one who has no sin." It is also obligatory to make up missed prayers according to the majority of scholars, as a precautionary measure.