I personally would have expected Senna to take the 1994 World Championship if all other events would have remained the same. But, would Schumacher have dared overtake Senna on the parade lap at Silverstone? How would Senna have dealt with three DNFs at the start of the year? There are many other questions that could be examined in this way. What if there were tyres at Tamburello, something which, despite several conferences with Gerhard Berger and the circuit manager at that very corner, was never debated? What if Senna had given the race a miss because of his emotions that weekend?
I would have expected Senna to have won at Monaco, Spain (Schumacher's gearbox virtually packed up), Britain, Italy, Portugal (Where Schumacher was excluded) and Japan at least- but was the Benetton even then too pacy?
As for 1995, it has been said that the Williams was quicker than the Benetton, but Williams strategy and many mistakes by Hill and Coulthard (as well as some great driving by Schumacher) meant that Schumacher won the world championship.
Would Senna have gone to Ferrari in 1996 instead of Schumacher? Possibly. But Senna had a tendency to hang on to a drive for a bit too long. Senna stayed with McLaren two years too long after resigning in 1991, and he kept faith with Lotus in 1987 when he had seemingly already realised that he wasn't going to win the World Championship with them- despite a seat at McLaren being pretty available. Its questionable whether Senna, having got himself into a Williams after two years of hard trying, would have left so easily. If so, Senna would probably never have won the title again. But, if he had stayed at Williams, then he would surely have won the 1996 title- and wouldn't have made the mess Villeneuve seemed to make of winning the championship in 1997, surely?
There are too many questions ultimately. He could well have stayed on three, but there was the potential for a maximum of seven.