More mobilization is impractical; the current mobilization seems to already be far more than the system can handle.

And as for straight out war...the war went hot in Feb. Russia has been holding nothing back in its (so far futile) efforts to defeat Ukraine on the battlefield.

And Crimea has been attacked many times already, it's clearly not a red line, nor has Putin expressed any clear "red lines". (Many red lines have been hinted it, many have been blown through without a response.)