Conte leaving is not surprising even without considering Abramovich.
He's just used to it.
He left us just at the beginning of pre-season after we failed to buy one of his targets, and after constantly mocking his players (he literally said that we were like toy tanks going against real ones, after we failed to make to the round of 16 in cl; with the same team that reached the final the year after) and our board for being parsimonious (other infamous quote "You can't dine at a 100€ restaurant with 10€")
I guess that ,after winning the PL with Chelsea, discovering that he can't spend gigamillions on the market is too much for his ego.