There are two answers suggesting melt. This is not a bad choice, and in many circumstances it is the one I would use. It would be widely understood and wouldn't raise many eyebrows.
That said, melt carries at least a little hint of a sense of temperature changes. (I think butter melts because the colloidal fats actually do change from solid to liquid with temperature changes.)
@JezW mentioned the noun liquefaction. I agree that in the noun form it is technical jargon rarely heard outside of science/engineering. I believe the conjugated verb form, liquefy/liquefied, is used more widely. (var spelling: liquify)
If the gel turns to a liquid completely in the absence of temperature changes, I would use liquefy.
If you squeeze a corn-starch and water mixture it will harden in your hand, but if you relax your grip it will liquefy again.
I left a jar of mayonnaise in the fridge for a year. When I opened it, it had completely liquefied. Do you think it is safe to eat?
If you don't use your hand sanitizer within a month or two, it might start to liquefy.
In the later two cases the implication is that despite stable temperatures, something else has caused the structure to break down - the solids spread through the liquid are settling, or are simply falling apart.
Evidence for this word being used outside of a scientific context:
The song "Liquefy," by the band The Servant: youtube link to music video
TLDR; I would consider liquefy/liquefaction to be the general term. It could occur due to melting, decay, decomposition, sedimentation, deliquescence, etc. In casual circumstances, people might use melt for any of these, but it has connotations of temperature change, and will sound strange if people know one of the other mechanisms to be at work. Liquefy is widely understood, and always means turns into a liquid, whether by chemical, thermal or mechanical processes.