The cost may not be worth the aggro. A 2011 (ish) N20 E89 Z4 with average miles can be had for around £5k now in the UK. Hopefully without a bust camchain/ engine!If it jumped a tooth it can and made a valve soup. Cranking it will just make it worse untill it totally eats all the moving parts.
Get another engine, do the timing chain for preventative reasons and youre good to go.
Just swapping can be done at a shed with basic tools. Plug and play.
Or even a nice N52 23i with a much more reliable engine can be had for the same money.