No, because he can still run as an independent in a majority of states. Most states final deadlines for ballot access are after the convention. If it becomes clear he won't be the nominee earlier, he could get on the ballot in even more places. If it looks like the RNC might deny him the nomination, he will probably start filling in the early states as a threat to the delegates. Ballotpedia has a list of deadlines, btw.
His optimal course of action is to run as an independent in some states and as a write-in candidate in some others, depending on the logistics.
For example, it's almost impossible to run as an independent in Texas but it's actually pretty easy to run as write-in. In some other state the opposite might be true.
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