It seems that just 2/3rds maybe of the Izyum front troops made it out, but without their heavy weapons. Their withdrawing columns have been filmed with drone video, consisting of nothing but trucks. I suspect that there was an agreement to let them leave without harassment, on the condition that they left behind their weapons, which they seems to have done.
Exactly - straight out of Sun-Tzus' playbook --> give the enemy a chance to escape without their weaponry and they will be routed.
Dedbeforehonor --> you should tell that to the Kremlin that they can withdraw from Ukrainian territory