The West will need to act
Of course, the West will need to be seen to be standing up to the Russkies, and standing up hard to them. Why? Cos otherwise what signal does it send to others who may wish to do a bit of military tourism? And what about those countries with whom we have Defence Treaties and Security Treaties with (think South East Asia) - what value will their bits of paper be if we don't support Ukraine, and show that we are willing to enforce respect for their territorial integrity.
This is a defining moment for the West - shame it had to be against a competent and unpredictable foe!
Personally I think that the West will come down hard with every instrument short of a military response.