Not very, I'd say. I suspect Senna would have retired on the spot.
This. As Sid Watkins said to him the day before, he'd won everything and had nothing left to prove. Barrichello's accident hit him hard and you know his reaction after Ratzenberger's crash. The only time he shook his head after an accident, I think, which is something considering how lucky Martin Donnelly was. I would not have been surprised if he retired there and then.
I disagree with comments I've read from time to time saying "Ayrton would have won 3 more titles if he had lived; 1994-1996". I disagree. The Williams in 1994 was nowhere near as good as the quote/unquote
"legal" Benetton, and Senna had two DNFs prior to Imola; an accident that wasn't his fault at Aida and an embarrassing spin at Interlagos which you could blame on the poor balance of the car. 1995; we all know Benetton cruised it that year. Easily the best car, coupled with the best engine. Some more wins for Senna, probably. 1996; It came good for Williams. But, if Senna had continued and my assertion is that it would have been two years of lukewarm performances, he would have retired at the end of 1995. Definitely nothing left to prove, and he would be approaching 36-37, a typical time to retire.
One 'What if...' I always find interesting is the story in Eddie Jordan's autobiography about how, before he signed for Williams, Jordan held talks with Senna where he offered him a 50% share in the team, full control over car development, guaranteed preference, the whole nine yards with all the trimmings; a way for him to gradually change from driving to managing. I've never heard this story as being confired as true, but it's a very interesting hypothetical. Barrichello and Senna racing side by side in the superb little Jordan 194? We can only dream.
What makes you think that the same safety measures wouldn't have been introduced after Roland's death?
This too. He's always a forgotten man. Regardless if Senna survived, things would have changed that weekend. Ratzenberger drove on rails into a concrete wall at ~190mph, in an era with significantly less cockpit protection, sidewalls and so on. That crash alone was a massive wake up call.
Max Mosley didn't attend Senna's funeral along with the rest of the paddock. He went to Ratzenberger's because he "felt it was important that somebody went to Roland's", which I find admirable.