I understand they undergo fasting but this is his profession and is there any loophole to skip one year to pursue his career
Khabib is an avid follower of his faith and there is no way he will be skipping that.
How can a person survive for 1 month without water? For sure he will have a substitution, probably some kind of "energy-kind" drink (not redbull or alike, but something with amino acid or creatine). Does muslims allowed to drink milk during Ramadan?
They can drink water after fasting and they will not even swallow the saliva during fasting. The idea of fasting according to their faith is that they will not eat or drink anything during the day but at night they can drink and eat anything they want.
I mean 249 main event is prolly the biggest match of the year and it's gonna go on behind closed doors without a huuuge crowd? Seriously? It's better to wait and get it on again at the end of the year. IMHO.
If by chance they conduct the fight behind closed doors it will probably become the biggest pay per view events in history as there are no sporting events right now and everyone will be tuning in to watch the fight and the loss in the live gate revenue will be compensated with the pay per view revenue.