Core devs won't agree with each other about the scaling proposals (because they have different goals) and Wladimir doesn't make the choice (if such is against his principles), thus there is an eternal lock-up on the issue and they'll move to work on other more interesting issues.

The average transaction rate will just level out at about 0.5 MB/block or half of the current blocksize limit (like it did when majority had 250, 500 and 750kB soft limits).  Some players in the economy will just leave to another projects or quit as they lose their confidence in Bitcoin's ability to grow, which in turn causes price to start trending down. There will be other forks as people get uneasy about about profits and growth getting wasted and Bitcoin will survive.

Really? Well.. no one knows.