up to 50% is fine. Ive run and posted the calculations before, but that is only a few revs per mile difference, which is perfectly acceptable for any differential

10000 miles does NOT tell us tread depth....

generally new they are 10/32...so if the other 3 are 5/32 or more you should be fine.

If you are concerned, replace the pair on an axle and retain the 'good' tire in your garage for the next time it happens. Then you have a used tire to add to 'the other 3' should it recur.