There was a gal who started out in my class as a first year medical student who was Navy HPSP. She loved the nighlife, she had to boogie on the disco 'round, oh yeah. Anyway, she was told to repeat her first year due to poor performance in multiple modules. It was a big mystery what the Navy was going to do with her, but I heard from a few of the Navy HPSP guys in my class that the Navy made her pay out of pocket for the year she had to repeat but then let her keep her schlaorship for the remaining 3 years (pending successful completion of the 1st year). I even saw her as a Navy intern a couple of years down the road (so it must have worked out).
So there is precedent for at least one of the services working with HPSP students who experience "academic difficulties". Hell at USUHS there was a certain infamous medical student who failed years of medical school twice and was still kept on and graduated. Of course this was all during the height of the GWOT (mid oughts), so who knows how accomodating the services are now.
Like other have said above, it would be best not to test out these alternate pathways. Buckle down and git 'er done.
