Hiya!
That factor does have to be weighed against the question of where is the fun in playing a dribbling vegetable for the duration of the time it takes to complete a more extended quest?
True enough, but then we start going down the whole rabbit hole of "If something detrimental happens to a PC, then the DM shouldn't have let it happen without providing a quick means of countering said thing"...which leads to "..and if we're gonna do that, then why bother with ANYTHING bad happening to the PC in the first place?". Slippery slope, IMNSHO.
What we do is the PC of said character either pulls out another one from their character book, or (more favoured) they take over the roll of an NPC hireling or henchman. Hell, we've even let someone play another PC's pet...on more than one occasion.
Anyway, my point is, is that sometimes bad stuff happens to PC's. It's part of the game. Is it "fun" to have you fighter reduced to a vegetable state? Not really. But without the possibility of it happening (or something equally bad), or having any such thing be 'easily' countered by simply "Oh, great, there goes 1 hour of PC time and 500gp. We get 500gp of X, then take an hour and cast Y. OK. Now lets keep going". Sometimes this is fine, and in some games I'm sure it's the norm. What I was trying to point out was that there are a LOT of "non-mechanical" means (pretty much infinite, seeing as it's an RPG) of overcoming "bad stuff" that happens to a PC.
If the group really wants to keep the PC played (as opposed to the Player taking over an NPC), then allow for a "temporary INT boosting herbal tea" or something. Have it cost some amount of gold for the 'rarity' of the tea leaves and/or liquid. When drunk, it puts the drinkers Int at 3 if it is lower than 3. If it is higher, it has no effect. Now the PC's have to keep the tea safe and have the means to boil water. That is enough of a drawback as the PC's adventure to find the 'Golden Mushroom' and all that. Playing a character with a 3 Int can be...interestingly fun!
Resorting to the more mundane 'mechanical means' misses a golden opportunity...

...to explore the more narratively magical aspect of the campaign. YMMV.
^_^
Paul L. Ming