Unfortunately, this desperation will not open up diplomacy, it will likely be at the cost of the people. They are not in a situation to take on such a large military force if they attack EU or NATO.
The point of these damaging sanctions is to not need war ever again in the future. If Russia, a nuclear power, cannot take Ukraine and cannot weather the sanctions toward success. It will tell the entire world that war is not needed anymore. That is a thing of the past for humanity.
Additionally, there's some very unusual resistance to Russian troops. It was Spetsnaz blue berets who airborne dropped to take this airport: https://news.yahoo.com/russian-forces-attack-airport-outside...
But were routed so quickly? The probability that normal Ukrainian troops could do this is quite low.
The probability that many other countries have their special forces operating in Ukraine is 100%. Obviously nobody will admit to this. The Russians probably don't realize this and is suffering these massive casualties because of it.