Hybrid battery water pump? '08 Nissan Altima Hybrid

My car started having issues a few months ago
and when I brought it in to get looked at the guy
said the water pump that keeps my hybrid battery
cool has failed. When I drove at high speeds
(highway) or just drove consistently for more than
20 minutes my check engine light, VDC light, hybrid
warning system light and one other light (I tried to
attach a picture but it's not letting me it looks like
an exclamation point inside a full circle) would
all come on and accelerating got much harder. I
would have to push the pedal all the way down to
accelerate. After turning the car off all the lights
would be gone but it would happen again if I tried
to go fast. I got an estimate for just under 1,000
dollars, which I can't afford right now all at once.
So while I'm saving, I'm still driving the car I just
don't get on highways and never drive for more
than 20 minutes (pretty much stuck in my city) but
so far that's been working fine. I have a couple
questions like how long will my car continue to run
before I kill the battery from overheating or will it
continue to run in this diminished capacity? Can I
use my air conditioner, I called the dealership and
they said they weren't sure but not to just in case
but I really miss my a.c. especially now in late July
so an actual answer would be great. Also, should I
be driving in the “B” gear or the “D” gear, when I
bought the car the guy said to just use the “B” gear
but from what I've been reading that seems like it
might not be true. Thanks so much for reading!