Is a person rewarded for doing good while committing sins such as abandoning prayer and sins of solitude? And do these good deeds remain in his balance after repentance, or do they go to waste?

The reward for a Muslim's good deeds is not lost if they die upon Islam, for Allah Almighty says: "{And whoever does righteous deeds, while he is a believer, will neither fear injustice nor deprivation.}" If they had sins, then their reward is weighed; if their good deeds outweigh, then they are felicitous, but if their bad deeds outweigh, then they are under the Will of Allah, for Allah Almighty says: "{Indeed, Allah does not forgive association with Him, but He forgives anything less than that for whomever He wills.}" As for one who repents from a sin, they are like one who has no sin, and the reward for their good deeds remains, even those that were nullified by the sin.