Upon surrender there are 3 options.

1. You are the only human player. An AI player will be declared the victor.

2. There is 1 other human player. He will be declared the victor. Your regime will be put to sleep.

3. There are 2 or more other human players. No victor will be declared due to your action. Your regime will be dissolved and all territory it occupied made neutral.

After surrendering and pressing next turn you'll never get back into your regime.

You can see all statistics after a winner has been declared and thus if only 1 or less human opponents remain after your surrender.