Advice wanted: Holden Captiva with dead engine.

Took my Captiva in for a service today with the check engine light on. Turns out the timing chain needs replacing but the engine is full of sludge (whatever that is). They are recommending a new engine with a quote for a reconditioned engine running close to 80% of the cost of an entire similar make/model/age/km's car. Is it worth the repair? Should I cut my losses and scrap it? Could I get another year from the dodgy engine and run it totally into the ground? Is that even safe? Is replacing an engine likely to lead to a lifetime of other issues? I really like the car and it is in otherwise great condition with good body, accessories, interior and wheels. It's only 7 years old with about 150,000kms. Any help would be appreciated, I'm not much of a car head. via /r/cars http://ift.tt/2rGfWKg