Silicone is generally crosslinked via one of two broad methods. Both involve the use of vinyl groups on the backbone. One method uses some kind of radical initiator like an organic peroxide and the vinyl groups will polymerize. The other is the usage of vinyl groups off the backbone of one polymer, and simple hydrogens directly on the silicon (aka silanes). In the presence of certain Pt catalysts like chloroplatinic acid, a reaction called hydrosilation creates alkyl linkages. In both cases these are very stable. I think you would find your direct answer if you google "thermolysis of silicone" but I think Si-C is the weak link.
B. Yes, up to a certain point.
C. Depends on the silicone, but a byproduct of silicone degradation is the rather brittle compound of silica also. As well as oxidation reactions, again depending on what your alkyl or aryl sidechains are.
D. Certainly alternate crosslinks could create a silicone that thermolysis to a liquid instead of making garbage, however I think "vulcanization" is a poor route. Rubber tires as crosslinked this way, and they certainly don't melt with heat. Thiols to disulfides are encouraged by the presence of heat and oxygen.