Make a point of posting a single message in guild chat every day with the discord link and stating that in x days discord will be a requirement for membership at that time, along with whatever other reqs you want to set. Use the daily message as a countdown, reducing the number of days each day in the message so it’s clear how much time is left for people to take action.
Once the deadline is reached, start recruiting and replace people starting from the lowest producers moving up until everyone is replaced that needs to be. This buys your higher producers additional time to comply and your guild doesn’t suffer a loss of production immediately by tossing them all at once.
It’s never a fun thing to have to kick people, especially if they’ve been with the guild a while & produce. But if they can’t be a team player and communicate in some way they aren’t doing you any favors. But you run the risk of losing good players if they perceive the guild is inundated with slackers or your reqs don’t mean anything. But with several weeks of posting a countdown for compliance daily, your conscience should be clear that you did what you could to include everyone. There are plenty of guilds out there needing people so they shouldn’t have a problem finding a new home
The only real flaw with this plan is if you have some non-English speakers who don’t communicate or comply because they can’t speak or understand what’s going on & are happy just to play by themselves in the guild in ignorant bliss. That would be an unfortunate but unavoidable casualty if you are adamant about having everyone communicate.
Whatever you decide, good luck! Being a GL can be both rewarding & a pain. Hopefully you find it more the former than the latter.