We've actually had two referendums on joining the EU in Norway, in both rounds there were a minor majority not wanting to join the union - but the politicians wanted to join.

Finland was more positive than Sweden, and Sweden was more positive than Norway, so the referendums were arranged with Finland first, with the expectation that some of the Swedish voters would vote yes if Finland would join the union ... and Norway last, expecting quite some Norwegian voters to vote "yes" not to become isolated from the other Nordic countries. But I digress. Main thing, politicians were expecting "yes", but got "no" - just like in the UK.

So the politicians made some agreements with the EU; for almost all practical purposes Norway is a member of the EU, it's just the tiny small difference that we actually aren't officially members of the EU.

The same could happen in the UK - the UK still for (almost) all practical purposes being members of the EU, except that they officially are outside the union.

Or, the "brexit" could simply be stalled forever, that's another possible outcome. Or, some concessions from the EU, and UK formally continuing as EU-members after a new referendum. That's would be the most rational thing (like you also wrote, Cameroon should have taken this route in the beginning).