Praise be to Allah.
There is grave major sin on this person because he continued for all these days praying without being in a state of purification. The Prophet (blessings and peace of Allah be upon him) said: “Allah does not accept any prayer without purification.” What he must do with regard to his prayers is repeat all the prayers that he did before doing ghusl.
With regard to Hajj, he has to repeat tawaaf al-ifaadah, because he did tawaaf when he was in a state of janaabah, and tawaaf is not acceptable from a person when he is in a state of janaabah. That is because the one who is in a state of janaabah is not allowed to stay in the mosque, as Allah, may He be exalted, says (interpretation of the meaning): “O you who believe! Approach not As-Salat (the prayer) … nor when you are in a state of Janaba, (i.e. in a state of sexual impurity and have not yet taken a bath) except when travelling on the road (without enough water, or just passing through a mosque)” [an-Nisa’ 4:43]. If he was married, he should avoid intimacy with his wife until he goes back to Makkah and does tawaaf al-ifaadah. In that case he should enter ihram for ‘umrah from the miqaat, then do tawaaf and sa‘i and cut his hair, then do tawaaf al-ifaadah. In addition to all that, he must also repent to Allah by regretting what he did and regarding himself as having fallen short and neglected the rights of Allah, and he should resolve not to do such a thing again. End quote.