The 960 and 930 are both the same footprint as your 870. Since you don't mention a service contract, chances are your repair might be extensive. I have seen both 960Q and 930 machines (own a 870Q - about 5 years old, and keep it under contract, no big problems to date, use the machine alot). The 930 is a slight upgrade to the 870 - and the "sewing advisor" panel, which you are familiar with, is identical. The 960Q has a different interface, using a stylus, and allows you to download new stitches via your computer and transfer them to the 960Q.
There is a BIG promotion on the 930 going on right now -- thru the end of March. With ANY tradein -- the manufacturer's suggested retail price is dropped to $1,299. You can see the details of this offer -- google Husquvarna Viking -- and when you get to the site, click on "promotions". This is really a great price for this machine. It's less than my "on sale price" for the 870Q back when. This is still alot of money -- and perhaps getting a quote on repairing your 870 might be worth thinking about. And do check all the features on the new one, to make sure it has those which you use the most on your 870 -- I could have missed something looking at it with my eyes, we all have different "must haves" on your machines.
Finding the warranty information on their website is difficult, I finally gave up -- do think it is 25 years on the motor, but don't know if labor is included.