I had something similar, I found using an iPad I was able to get into the Page Editor quickly, by mashing the Edit button, before the site loaded fully (couldn't get in quick enough on PC). If you can get into the editor fast enough the html code won't run and you can make your amendments to fix the issue. It does take some attempts though, keep refreshing and hit Edit quickly.
I've also seen an issue where a widget 'errors' and going into the Page Editor to remove it then won't allow saving of the amendments. The page is in limbo.
For me, Nested Pages is a must when putting in anything complex, much easier to resolve issues when separated away from the affected site. I have a dedicated site for nested pages components and can correct issues there, causing little impact elsewhere on the platform. If you do have to bin a nested page, then at least it's not a whole site, just a page.
Just sharing my rookie mistakes, if it's helpful to anyone, I'm learning from them though.