Yes and no. Theoretically you vote for the party and the leader of the party is PM, whoever that leader is at that time.
Major didn't, Brown didn't. Major won the next election, Brown lost it... Such is life.
We don't elect our PM's so to say that because the PM has changed, we have fundamentally lost OMOV, is not quite right. Whilst people may have balanced Miliband with Cameron, essentially their vote was for a MP, not a PM.
So, in essence, a change in leader changes nothing in the democracy.
Of course if the leader feels there is a chance to gain something from a snap election, that's another matter. Were I May, I would be very sorely tempted to call a snap election. Far more Labour voters voted against the wishes of the party than Tories, who were split very deeply. Also Labour is in total disarray right now. Me? I'd call an election for 4 weeks time. Let Labour destroy themselves in a fit of fear and take their votes.
Be careful what you wish for, a huge Tory majority led by May is not something I'd like right now. If we give a bit of time for Labour to get all the bloodletting out and back on balance again and they could put in a good showing. Right now they're going to get steamrollered. The only think I can see a snap election doing right now is letting a lot of UKIP MP's on the floor. Of course I would not mind that. You, on the other hand, would be a touch dismayed I think. Although you would enjoy the spectacle of them trying to renage on their promises I'm sure...