how long has it been since his last round of meds. if you are able and he isnt going drastically downhill id wait a full 2 weeks between doses of the velvet meds and the fungus eliminator. certainly wont hurt to dose for finrot/fungus if hes having a hard time clearing it himself (ie immune system being low).
when you say silvery grains on his body what do you mean by that? are they between the actual scales themselves (if yes id be tempted to say once again normal color-a truly solid red betta is very rare. often they have blue/pink/purple/silverish spots between the red scales. if they are raised and look like grains of sand stuck to the fish might be ich, but the velvet treatment should have taken care of that.
he does not look bloated at ALL in the photos. in excellent body condition actually (fins dont look too bad either). yes, his swimbladder may be permanently damaged (it does happen) but so long as he can swim ok, got to the top for air and eat his food he should be fine-although look a bit pathetic. it will not outrightly kill him. he will just be a little "special". it is also quite normal for them to constantly hang out in the same spot. if he were hiding and not occasionally swimming around (even if he goes back to that same spot) then id be watchful for signs of illness. they are lazy as they get old.
cheers