I don't get it. Germany is the most dependent on Russian gas and Angela Merkel has been the one most dragging their heels on even sanctions. Why would the open letter be addressed to her? Why all the Iraq WMD comparisons when the open letter even admits Germany didn't even want to get involved there? The Baltics states will be the only ones pushing for direct action, and Britian the only one able to take any.
In fact reading through their previous open letters they all seem a bit confused. The only common thread appears to be Russia should be allowed to deny Ukraine access to NATO and a bunch of odd vaguely but not really related historical incidents being thrown in to make the letters appear longer. Their language such as calling the separatists "anti-coup federalists" makes the letters appear to come from a Russian rather than a non-Russian perspective.
I think the "bury out heads in the sand and hope Russia doesn't do anything" is a little late. He's already invaded Georgia once and Ukraine twice. His home propaganda is a resounding success, with the people prepared to back future invasions, and the parliament is filled with his puppets. Ukraine joining NATO or falling under New Soviet rule seems inevitable and they probably prefer the former.