"Preferably run your own server" has nothing to do with remote-only work or setting up a team for success remotely, it's just dogmatism.
A remote-only company hosting its own IRC instance is in no better position to succeed than a remote-only company reliant on Slack for communication. Yes, services shut down. Yes, DDoS attacks happen. But buildings also lose internet access, people trip over cables, etc. The weaknesses are different but one is not inherently better than the other.
Force the sync mechanisms and processes to be "remote only" oriented.
* Instead of meetings, have discussion threads and deadlines for achieving a decision goal.
* Instead of face time, document requests and responses in a more formal way (and have an informal channel as well for sounding out ideas).
* Use a corporate owned chatting mechanism. IRC, Slack, some xmpp nightmare, just find something that works. Preferably run your own server.
* Maybe some jobs where already over capacity, divide the workload further.