Yeah, the problem is, who is a monarch supposed to appeal to?
-The West has no interest in spreading monarchy by this point (and most of the main players aren't monarchies, even within Europe), so it wouldn't appeal to Poland's new foreign allies/benefactors
-The anti-communist movement in Poland had never been monarchist, so they wouldn't want to impose one.
-The remaining communist sympathizers obviously wouldn't be monarchist
-There is no indigenous monarchy or monarch-in-exile, so there isn't even a group of that sort.
So it won't be a unifying factor, anymore than Emperor Bokassa declaring himself Emperor of the Central African Empire did anything to solidify his nation.