The MPL is just a variant of the Integrated course and graduates have a CPL/IR with frozen ATPL credits exactly as the others do. What they don't have is a single pilot IR or MEP Class rating, but they will have a MP Type rating. If they walk straight into a job thats fine but if they don't, there is not much else they can do.
On the instructor front, its going to become much more difficult under EASA to become an IRI unless you have airline or air taxi experience. If you want to teach for the MPL you need to be a FI ME with IRI, complete the MPL Instructor course and of course have 1500 hours MP experience which largely means only Ex airline pilots will qualify. Teaching in Simulators, you won't be able to claim the hours for anything either and keeping current may also be problematical as the only flying on the course is SE. Goodbye the career instructor.