Truth is, all brands and models in the consumer all-in-one space have roughly the same MTBF (mean time between failures), and none of them are immune to it (Asus, Netgear, TP-Link, etc.). Sure, you have model and serial runs that may lie a bit outside the mean, but the overall average numbers are what they are, and there's isn't a single model which breaks the bell curve once a sample size gets large enough.
That being understood, onto the immediate solution. Given then time crunch, I would just Amazon Prime whatever Asus you prefer based on features and compatibility with Merlin, and go at it again. This time, though, go on Amazon or eBay when you have the chance and order an extra AC adapter, so if/when this situation repeats itself, you can swap that it in to eliminate the chance that the adapter is the problem, as quite often, it's the adapter that gets flaky and/or fails, not the router itself.
Beyond that, a longer-term solution would be to come at the problem from a completely different angle and run beefier hardware via discrete components (separate wired router, wireless AP(s) and switching). That won't stop a hardware failure from ever happening, but with the right product selection, you can certainly improve the odds. I'd keep it in mind for when you have more time to plan your next upgrade and learn a bit more about networking along the way.
