Do the missed prayers of one who stopped praying for four years due to depression, then repented and performed 'Umrah, become null and void?

Performing Umrah (definition) does not absolve one from the obligatory duties owed to Allah. The majority of scholars hold that intentionally missed prayers must be made up immediately, unless doing so would harm one's body or livelihood.

Zakariyya al-Ansari said: "It is obligatory to make up missed obligatory prayers... if they were missed without an excuse, their make-up is obligatory immediately."

Al-Dusuqi said: It is sufficient to make up two or more days' worth of prayers in a single day. Some scholars are of the opinion that make-up is not obligatory, and that repentance and supererogatory prayers suffice, but making them up is more cautious.

Depression, or organic and psychological illnesses, are not an excuse for abandoning prayer as long as one's intellect is sound.