HXTAL is made to not come apart very easily and it definitely lives up to its reputation.
Probably the easiest way to get rid of a wayward HXTAL bond is to re-anneal the entire piece. The high temperature of annealing will burn off the glue and leave a black residue that can be polished off the glass (it will stink up your entire shop too). HXTAL will break down around 500° F.
If that's not an option, then you can also try the ATTACK epoxy solvent and be prepared to have a lot of patience. The ATTACK will dissolve the joint, but on HXTAL it takes a very long time and it will stain your piece (a lovely purple shade) so you'll have to do some polish clean up afterwards.