acl rupture

[msk101]

Because it's uncommon to just rupture an ACL without damaging some cartilage or other ligaments at the knee, if your knee buckles when you're running at high speed you do risk damaging further other ligaments and the cartilage (menisci) of the knee. Your physio will be able to assess your knee and give a fairly good estimate on whether you have any ACL left or not, and whether there's much damage to other structures, particularly the MCL and the medial menisicus. also the MRI report should detail partial or complete rupture, and other damage.
Other sports you can do to minimise further damage are cycling, elliptical trainer, swimming (but no breast-stroke and no flippers on), you might be good to do some straight line jogging but hard to say without seeing you and assessing knee, and you can do all your upper body work as per usual. you can also use a rowing machine but making sure you do NOT lock your knees out at the end or fully compress them in the crunch position. if you're keen on group classes at the gym then try for a spin/RPM class. your physio should also have you on a program of specific hamstring and quads strength and balance exercises which you can get to a very high level and are hard work!
ACL rehab is long and boring but rewarding in the long run.

[physiofixme]

I think the advice you have been given so far by msk101 is excellent.

If I was to put my 2 cents worth in I'd say cross train from now until the surgery and don't play. You really need to preserve your cartilage and other structures of your knee. If you run too much on an unstable knee you can do further damage which will mean more problems long term.

Keep up your fitness and strength with gym work and cycling.