Yes, even with its slightly more elevated grounds, Lysychansk does not seem to have the prospect of holding out longer than Severodonetsk. Once all the grounds near Severodonetsk are cleared (maybe in a week's time), they will start their heavy shelling of Lysychansk and will probably crack it two weeks after that. What is more, there were rumors that the Russians already took Svyatohirsk. If that is true, than the Russians will go all the way to Slovyansk from the north very soon. In a month time, it will be all over. Even if Slovyansk and Kramatorsk are still in it, they will be cut off and pounded to pieces.
I used to wonder why the Ukrainians in Donbass did not retreat to the Western Ukraine. Now I am of the opinion that they don't really have that option. Having lost most of their armor and out of gas, they will be destroyed if they try to leave the fortified positions they currently occupy and run in open country to the West. Bridges can easily be blown up. Now you are out in the open waiting for the attack aircrafts to show up.
Furthermore, I don't believe a big offensive is coming from Western Ukraine. Even if NATO can muster the equipment and can round up enough people to fight(highly doubtful), they will have only been trained for a couple of months and can barely hold a rifle. What is more, they can't even train in open ground without being hit. What the Ukrainians lack are able bodied, trained and motivated men. Most of these would have already died in the Donbass theater. If you recall how the Saudi arm forces with the best armored vehicles and tanks were defeated by the Houthis in Yemen, motivation is a big factor and so is training. Sending a hundred thousand (assume there is enough equipment to equip that many) slightly trained men against a professional arm forces of Russia which have long range rocket artilleries, air force and longer yet range missiles, which are well led will just send them to their deaths, no matter how well equip they are.