if russia wanted to make gains to offset izyum they needed to mobilize like yesterday. clearly there is no other way to win this now for them. this is what happens when you want to avoid hard decisions. Putin seems to be making a lot of mistake here, lucky for China i guess.this is one of the few good things they're doing. There is some critical land in Ukraine but having the conquered people is a goal, if implicit, in a way that it wasn't for any other war except maybe Sino-Japanese WW2.
The problem with losing Izyum is that it controls a major bridgehead, refer to map:
Izyum is at the confluence of the Oskil and Siversky Donets rivers, a highly strategic position. Control it and control a bridgehead over the Oskil and Siversky Donets into Luhansk oblast. Bad. If Russians lose Izyum with no corresponding gains elsewhere despite Ukrainian reserves being redeployed away from the southern axis, it is a loss for nothing. But if the Russians manage to make gains near Mykolaiv or Zaporizhia then it will be a trade. A bad trade for Russia, but still a trade rather than nothing. Losing Izyum, while not as devastating as losing Kherson, is a loss of a very important location.
I have to hand it to the Ukrainians on this one. They had the courage to sacrifice a huge amount of troops in Kherson and special forces at Zaporizhia to make gains at Kharkiv. Turns out the Kherson offensive was indeed a feint. A huge, expensive feint, but a feint nonetheless.
best thing russia can do now is mobilize and hopefully double its army's size by next february, that would allow it to not only threaten sumy, but also zaprozhia and dnipropetrovsk.