It'll pass and be a bit harder for Republicans to deny Puerto Rico statehood and federal representation than they do to the District of Columbia. But I'd still expect them to stall its official recognition of statehood unless there can be some arrangement to ensure Puerto Rico isn't completely represented by Democrats.
The last time new state was admitted was kind of a mutual compromise betwen parties not to upset the balance. It was assumed Alaska will be a Democratic state while Hawaii a Republican one. Of course it flipped rather quickly (I must say I don't quite get the idea of Hawaii being a solid GOP state, given consequences of the Hawaii Democratic Revolution of 1954.)
Puerto Rico is the only territory large enough to become a state. There's no other candidate to balance this, especially a GOP-leaning.
The only possibility for a scenario like that would be to divide a US state or forge a new state from two or more existing states. Considering how unlikely that is, the GOP will have a choice after June: either admit Puerto Rico as a state, knowing they'll give more power to Democrats, or stall.
