That's why we can't just ease off sanctions soon after Russia packs up and leaves, assuming that deal is made. Russia is the jilted ex- who is blowing up Ukraine because "if I can't have her, nobody will!" Any rollback of sanctions needs to be very gradual and frankly, I'd prefer that Russia be treated as a pariah state if possible (but keep the oil and gas flowing LOL).
The good news is that the U.S. helped rebuild western Europe post- WW2. It'll cost a ton of money to do it in the modern era, but probably can be done for much less than it costs to rebuild our own aging infrastructure.