Effectively, the Republic has been destroyed, and the Resistance is left fighting the First order while horribly outgunned.
I did not get this from the movie at all, I sort of assumed. I just figured they dealt a significant blow to the Republic, but wiped them out completely? So essentially for EP VIII we are back where ANH started: evil Empire (First Order) effectively rules the galaxy and the Rebel Alliance (Resistance) fights against them. Ugh. Enough with the rehashing the OT.
Consider the alternatives.
The Republic is not crippled but now has full cause to go to war (and the resources to do it). We don't know fleet sizes, but this could go one of two ways.
Either the Republic far outnumbers the first order. Then the rest of the movies involve the republic just mopping up the mess. No fun. No excitement. Just an overwhelming force rolling across the galaxy.
Or the 2 sides are more evenly matched and we then get a rehash of TCW/AotC/RotS. That could be interesting in its own rights, but it would still be something similar.
In any case, it's Star Wars. So we're going to get a war somehow.