There are actually only about 12 true "winner take all" states. The rest are either proportional (some with a threshold to receive any delegates), or they are a hybrid where the winner of each congressional district wins the delegates for that district, and the overall state winner wins a few extra delegates. California follows that model, for example. So if Trump, Cruz and Rubio continue to battle it out past March, it is likely that none of them will be able to get a majority of delegates before the convention.
While I acknowledge that is the case, the historic trend that I observe is to use the early states to narrow the field quickly. Not sure if that trend will remain true during this year’s primary. I can see a scenario where the early proportional states create an ongoing three way tie with the winner take all and/or hybrid states consolidating around one candidate. It would then be possible for that one candidate to have enough going into the convention to win the nomination. This is more of what I see historically,.
It is also equally possible to have a three way split that is close enough that no one candidate gets the nomination automatically. I fear this scenario as this would allow the GOPe to come in and rig the system during the convention.