[Baz]

1. cut off the damaged 45 fitting as close as possible to the fitting on both ends
2. this should leave to the right side the .9" you mentioned as a 3/4" stub out
3. then trench backwards along the left side pipe (as shown in the pic) so the pipe can be moved to each side a few inches.....go back at least 12-18"
4. then cut that pipe about 12" back from where the damaged 45 was
5. with a new 3/4" coupling - PVC glue on a new section of 3/4" pipe - use thin wall - not schedule 40 - a bit longer than what you removed - 15" probably ideal
6. then glue a new 3/4" 45 onto the stub out and then let it sit for at least an hour to set up good
7. move the new piece of 3/4" pipe over and above the new 45 - and make a mark on the pipe where to cut in order to properly fit into the 45. It's OK if it's a hair too long as the added pressure will help hold it in better. Just not too much - a very fine line here
8. then cut where marked, glue it in, then let it sit for a 1/2 hour - then test

When you do the last connection you will have to bend the left side pipe a little to get it in the new 45 - lifting the pipe and connection up a bit always helps when you do this.

Good luck!