Had my atv roll out of the truck and land upside down. since then i have noticed the oil has a gas smell and is thin. Could gas have leaked into the crankcase or could there be other problems.

 

If I were you, I would drain and flush everything. Oil, gas, coolant. Thin, milky looking oil is not good. If, after you drain and replace all fluids and you get the same look to your oil, something is seriously wrong, and needs to be fixed ASAP.