Sounds like we are all going to miss an opportunity to meet up in Budapest as we would all have been there about the same time.... I guess still may... but looking doubtful.
I could be mistaken, but if they cancel the flight, will they not put you on the next available at no charge. The next available might be June. In that case I get June tickets at April prices?
Anyway...... Things in Budapest are not "bad" but a lot is closed. As their outbreak seems to be trending behind the other countries in the area it is conceivable that it could be worse in April. If its your first trip, might be better to wait so you can really enjoy it.
Plan B for me, if going to Budapest will require a 2 week self quarantine when I get home, then maybe when I get to Istanbul I change my ticket to someplace outside of the Schengen Area ........... or maybe i just wait till things cool down and go to Budapest when the "ban" is lifted.