To be fair to Senna, at the time Lotus where hardly able to put together 1 car that could last a GP, try to run 2 top line drivers would have been beyond them, Senna knew that and blocked Warwick, I don't belive the Lotus mangement at the time fought very hard to get Warwick.
Not to sure how Warwick would of faired anyway, apart from his Toleman drives he never set the track alight in F1, his time at Renault was spoit by a poor car, but the best drivers always make a poor car better, right ?but did quite well in Jags and Pug's.