I beg to differ. Bitmain may have the majority of the hashing power of the whole network, but the fact remains that there are still numerous miners doing their part diligently, alongside other nodes so yeah. Bitcoin is not so reliant on Bitmain nor any other mining companies as the network is designed to adjust depending on network conditions.

On the other hand, this happens every once in a while on Facebook's data centers for routine maintenance or any other reason, as was to be expected on centralized servers.