Have we considered yet what happens if this invasion is repelled?
For starters, the Russians aren’t going to be repelled back to Russia. Ukraine at best will hold their cities and hubs. Russia has been building up their logistics within Ukraine since they started to take territory, so not once do I believe that their invasion has slowed down, it goes on as per schedule, they have a new doctrine now.
The question is what are they setting out to achieve, many have theories, and Russia have many options, but whatever they are planning on doing will involve separating Ukraine.
The separatists will advance and strengthen their domain in the East, with Russia providing military aid and support, Russia takes the South and occupy the Northern and North Eastern regions, sieging the cities, coercing Ukraine into an agreement by whatever means necessary. Ukraine, though the Black Sea ports are crucial, would place emphasis on holding the West, and Kyiv (which is not in the West), but central, and attempt at repelling the Northern and North Eastern Russian positions as long as they possibly can. Ukraine will take time to deploy their reservists, and its conscripts need to be prepared, but they all will inevitably hold positions.
I can’t see how Russia will want to occupy Ukraine in the long term, it would cost them almost all their troops, and will be economically exhaustive, and they still need to protect Russia, so I don’t see this happen. They have a better chance at controlling Ukraine by installing pro-Russian puppets in the respective regions. To have a look at a 2014 illustrative map,
which could be indicative at how they will go about now, but they invaded in the North, and have already taken Sumy, moved on Chemihiv and Kiev. It can be assumed that they are planning on taking all the regions along the Dnieper, but to take Ukraine as a whole could be an ambition too high. I don't know how Russian support has since changed in Ukraine. I don't know, but this invasion could carry on, weeks, months...
It is best to wait and see what happens. Who knows, the UN could collapse, NATO could include Ukraine... but I don't believe that Russia's economic partners will come and bail them out with troops. The world is a strange place, and Russia put it on themselves not to be trusted.