Tripoli has been completely annexed by the mamlukes. If I press F to search "Tripoli" only the province (not the nation) shows up, so I know for a fact they do not exist anymore. The cores are still there and will run out around 1544 (currently 1500ish). I took the lands with the intention of releasing Tripoli as a vassal to feed more mamluke lands, but in the release vassals options there is no tripoli option! Every other vassal core is there though and I never had trouble releasing any vassals in any of my previous playthroughs of 100s of hours of play. Wtf?