Hi
Welcome to the MedHelp forum!
Well, theoretically as surgeons have told you, the titanium plate can be removed. How much the bone flap has healed can only be judged by a surgeon who can examine your wife.
Over three years, yes there will be healing and fibrosis, and the bone flap will regain some strength. However, multiple craniotomies, radiotherapy, chemo and other such treatments will have their long term effects.
Please discuss with her treating doctor. Take care!
These questions are best addressed to the surgeon. If you want to do some reading on the type of plate that was used, you should find out the real name of the plate, because rose plate is not a useful lead.
With the correct terminology instead of the layman's terminology, you could use Pogofrog search engine to look for information.