Lookleft,
I would argue that if you haven't made every effort to obtain the latest TTF approaching your latest diversion point, you could be held liable for some offence.
If I recall correctly, the investigation into the Adelaide-Mildura diversions by a couple of 737 concluded (amongst other things) that both the airlines and the pilots should have been more proactive in monitoring the weather.
I've been involved in more than one situation of landing a airliner in poor weather with min fuel because we ran out of options. All when I was in the RHS. I'm touching wood here, but since I've been in he LHS it hasn't happened. I do my best to make sure it doesn't happen. And intentionally not updating weather in case it's gone downhill doesn't fit well with that philosophy...
