Blown Head Gaskets/ Motor?

No need to replace the engine if its me I'll cut of the headbolt and go from there

There are inserts available that would repair the stripped threads.

This is a common Cadillac problem with a common fix. First I'd wonder how your mechanic knew a bolt was stripped if he hadn't started on the job already. Perhaps he's making the assumption because this is so common.

It could be he has done a bunch of them before and knows how frustrating the job can be. It could be he hasn't done any and doesn't want to invest in yet more expensive specialty tools. It doesn't mean you need to switch mechanics, just find a different shop for THIS repair. Your best bet might be the dealership or an engine specialty shop if you have one close by. Either of them will be experienced in this repair and have the necessary tools.

Yup, getting a second opinion is the best in this case as the mechanic (p.I.T.A or the engine?) Is reluctant to do the job and requestiong him to do the job is not a good choice, unless you wish to replace the engine.