Alright, first things:
1. Compression test- if the engine is having compression issues, this would be the most obvious route, start cylinder 6 and work forwards, the 6th cylinder is often the lean one
2. The turbo, if it's not getting boost, have you checked all the hose fittings/ vacuum lines for leaks?
Before you start going off replacing an engine, look for any possible reasons why the turbo may not be boosting
As for compression, if you do have an issue, than the engine would run like shit and you'd be struggling to drive it
It should idle rough, have poor fuel economy, blow more smoke, etc
There are a lot of possible reasons for why a turbo isn't boosting, but yes, first things first, ask for the compression test and ask them to tell you which cylinder is down first
otherwise, if you can provide more information on how this came about, other characteristics, then it's very hard to generalise without trying to break down more specifics on what the car's behaviour is like, i.e, how it idles? How does it drive normally? how does it drive under-revs/ load? does it stall at certain speeds?
Once we can start pin pointing the small things, you'll get a better idea of if you need a new engine? or whether or not it's as simply as a loose vacuum line, fault AFM, injector, etc...
Hope this helps mate, i'll keep an eye on this thread and help you out as much as i can