Re-liquefying under heat treatment I don’t know but if you can forego that requirement, I would recommend E6000. If you do use it make sure to apply and allow to dry/cure in a well-ventilated area. It’s a great adhesive but has its fair share of carcinogens you don’t want to be breathing in..
Can confirm, e6000 smells amazing (and sticks stuff together reel gud)
I'm not sure there's a good adhesive that will accomplish this. What's the shape of the earbud? Could a piece of heatshrink on the outside accomplish it?
Hmm… I may be able to similarly get away with a slim strip of electrical tape. Won‘t look good, but I don‘t really care.
A glue used for phones is probably good for you, but it's hard to say if you can soften these with heat: https://www.screenfixed.com.au/top-14-best-mobile-repair-glue/
See if the design will allow for some other way to secure it, like using a small screw as an example. This will take some creativity and caution, but may be a better option if you think you will need to repair them again. (Adhesives have a tendency to not allow for future repairs.)
Share tips and tricks to keep people from throwing out that broken item. Repair before replace!