It’s dokuwiki.

If you want something that works very well and is quite convenient, I can recommend the Scaleway S3 Glacier storage. If you only need a few GBs, it will only cost a couple of cents per month.

If anything, I feel like Nextcloud Mail is the thing that’s going to end up being killed, not Roundcube. Nextcloud doesn’t exactly seem like a company that would buy a superior product just to kill it off.

I do agree that adding some kind of backup option is probably a good idea. For many people, losing their email account would mean being locked out of basically all their online accounts (or, in case the account gets compromised, it would mean that all other online accounts would now be compromised too). The majority of people do not use password managers or 2FA, and I’ve made the experience that many people simply cannot be convinced to make online security a priority. While I’m also a FOSS and online privacy advocate and use tons of self hosted services for that reason, having some way to regain access to their Google account is almost certainly worth the extra data point that Google gets access to. Especially since the likelihood of them already knowing about your phone number is basically 100% if you are logged in on an Android device.