My mum has a 7 year old (we think) cat with no teeth, he hasn't had them since we found him, as we think he was kicked in the face, his jaw has also healed twisted where it was broken (he was also covered in fag burns, hence the kicking theory rather than a car). Despite this he is allowed out (he goes loopy if he can't get outside) and is an amazingly good hunter! (I have rescued many mice and birds just very soggy and scared!)
It never occured to us not to let him out, just because he is missing his teeth, if he only had the 2 left then like you said I can't imagine they did much anyway?
As long as he has healed from his op and is eating well then I would let him out and about, but thats just from our experience with Mazza.
Hope that helps and hope his gummies are feeling better soon!
Jen