In the following window that pops up you can uncheck base and restart factorio.
yeah, I know, don't do that then.
When the game restarts you will then be greeted with this error
You are now stuck in an infinite loop at that error.I thought 0.14 gave a warning when base was disabled and provided a way to re-enable from the warning dialog or try to continue without it?
Fun Fact: if another mod is broken and causes that error to appear then click on disable all mods also seems to disable the base mod as well. Thereby screwing you being permanently stuck at this screen again. The disable all button really shouldn't disable the base mod too...
[edit]
0.14.23 Does provide an warning when the base mod is disabled but not until the main menu is reached. Starting with 0.15 you cannot reach the main menu while base mod is disabled so the warning can never be shown.
[edit2]
Fixed images and stuck them behind spoilers to save space.
[edit3]
Also if you disable the base mod in the mods menu you also get stuck in the error loop but that should be obvious by now.