That's higher mileage than others that have had total trans failures soon after flushing the ATF (few really) but it's a gamble. If you do nothing, the trans will fail but perhaps a later time, mileage? Changing the fluid will either help it OR cause total failure soon afterwords. Most cars that we do trans flushes to (lower mileage, usually recommend at 50-70K mile service intervals when it starts to look dark) never have problems afterwords. I've also done it to higher mileage cars too, no problems.
Last summer we did a flush to an AWD S70 with about 85K (very dark fluid) and days later his trans failed when hot, car wouldn't move until the fluid cooled off and he wasn't exactly happy (understatement) but there wasn't anything else we could do besides replace the trans.