Are the prayers performed with tayammum acceptable for one who is in a state of janabah and feared illness from ghusl, then later performed ghusl and completed the prayers?

The person in a state of major ritual impurity (junub) must purify themselves with water. If they cannot find water or fear harm from using it, they should perform tayammum until their excuse is removed, based on the Almighty's saying: "then find no water, perform tayammum."

Therefore, if you were able to heat water and bathe with it before the time for Fajr prayer expired, but you did not, and you prayed while in a state of ritual impurity, then you must repeat the Fajr prayer and all prayers you performed without ghusl, because they were prayed without purification and without a valid excuse.

However, if you were unable to heat the water and feared the time would expire, so you prayed with tayammum, then the obligation has been fulfilled, and you are not required to repeat the prayer. But regarding the rest of the prayers you performed without purification and without a valid excuse, you must repeat them and repent to Allah for this negligence.