tar/felt paper wet between floor & subfloor

widowoman

I recently discovered water leak in wall between kitchen & bath. Had fans blowing for over a week now, top is dry. Had to cut out the damaged top layer [waferboard] & discovered the tar paper held the moisture real nice. Fans now blowing on subfloor [also waferboard] where the fridge was.
My 1st question is, am I going to have to cut out the top layer of bath floor also? or will it "eventually" dry as a friend suggested? It looks ok, but know it is wet in between also.
Second question: the floor under the tub is particale board. It feels dry, but is as soft as a marshmallow. Same friend says not to worry floor joists will hold it up. True, I know, but would like to replace if possible without too much hassel, want to sell this place soon.
Is there any way to replace or harden the particle board under a 1 piece fiberglass shower/tub insert?
Thanks for any expert advise

joecaption

There is 0 ways to fix partical board. Once it gets wet one time it's trash.
Remove all of it and replace with Advantec subflooring.
No felt needed between it and the underlayment.