Yes your screws should back out easily.
The good news about the glue joint is that the edges of plywood often doesn't glue very well so the board may not be bonded to the poplar particularly strongly.
To break the glue line, if you have the right type of clamps you can reverse the heads and use them as spreaders. If not you can simply knock them off using a block of wood (softwood ideally) and a hammer or mallet. If using a hammer work in from the ends.
With a bit of luck the joint will just pop open and you won't tear any face grain off the poplar or out of the edge of the plywood but that is a possibility, depending on how well the surfaces were prepped ahead of time and how strongly they were pressed together while the glue dried (high clamping pressure gives much stronger glue joints with most woodworking glues).
Even if you don't rip off any face grain from the poplar the inside face will need to be cleaned up thoroughly before you glue again. A light skim with a hand plane, scraping or thorough sanding will all do what's needed.
Just a bit of sanding may be all that's needed on the edge of the plywood.
Note: you'll need to drill fresh holes for the pocket screws on the right leg so you'll need to move their positions slightly to one side of the existing ones.
Kudos for re-doing this by the way, many people would have just left it!
For a future project, a rabbet (UK: rebate) or dado (UK: housing) for the plywood edges will give you automatic registration, provided a neater and stronger join and make finishing easier.