SQL Server R2 and HyperThreading - Max Worker Threads and performance
I've seen failure to manage worker threads imperil more than one instance on various versions of SQL Server, at multiple businesses. The net result is memory pressure (which can manifest in different ways). In your case you can see clearly that a worker didn't yield, and what would be forcing it to yield is memory pressure. I haven't seen that result in a total FE like you've got, but again, memory pressure can manifest differently.

Set your workers to the appropriate level based on this MSDN article. Once you do, I would not be surprised to learn it solved your problem completely.

As for disabling hyperthreading, I don't think this is a good idea but opinions vary greatly on the topic. For sure I don't think it's related to your problem though.