The other disk has the exact same probability of dying as the one you just replaced ... same I/O patterns, same duty cycle, same temperature, same hours of operation, etc.. So don't dismiss it as being a fluke.
I would not do anything to rock the boat at this point, like turning it off and powering up again. Power cycles are pretty stressful. Personally, I would perform a full backup and order a replacement disk and make it a hot spare, just in case.
After the backup is complete, then you can try a power cycle, assuming Dell doesn't get back to you sooner.