For a young company that is challenging the established market, there are two typical success scenarios (from a financial perspective). One is for the company to grow and get the upper hand on competition (examples Google and Apple). Another is for the company to be acquired by one of the established players. What is the more likely success scenario for Tesla? And who would be potential buyers in the second scenario (and why)?
If you know Elon's view on the matter as long as he is in control an exit is not an option. Partnerships yes, but not selling out.
Many would argue that Elon sells his companies based on his history. I don't think this will be the case for Tesla or SpaceX because these are his two babies. In his interviews he talks about making life interplanetary and solving the energy problem on earth. But to entertain your thoughts, Diamaler and Toyota would be the two biggest potential buyers if something like this were to occur.
Tesla having such a big potential of growth (since Model X and Gen III are going to be produced in the following years) I don't think that Elon is even considering exit.
Not any time soon when EV are 90% worldwide sales then maybe. He will not sell out and let other ICE mfg kill it.
Exit by merger with Google (now Alphabet) *had* been discussed. I don't think Musk will allow a legacy automaker to take the company over. But if there's a huge offer from one of the tech companies (Google, Apple, Amazon), *which would leave management intact*, then they might consider it.