Repair Marin Hawk Hill (cracked frame) or get new bike?
A new similar bike would cost ~1500 €/$/GBP, right?
For half the price, you get a new frame, a new shock, all your old&amp;used parts (in which conditions are they)?
No brainer:
If you think your parts are worth at least 750$ and you can sell them for more than 750$, sell them and then buy a complete new bike.
If you think your parts are worth less than 750$, accept their offer (or find a better deal on a compatible set frame+fork)