Talk to a family law attorney in his county. Even if he doesn't do it, he should get some advice. Pay the $300 consult fee and get some knowledge.
General advice:
-If worried about spouse emptying accounts once news is announced, open up an account in own name and transfer half to that account.
-Run a credit report to make you sure you're aware of all debts in own name/joint name. Remove spouse from all joint credit accounts.
-Show up to all PTA meetings, dr appts, baseball games, whatever
-Scrub social media accounts
-Be prepared to spend tens of thousands of dollars if spouse wants to contest.
Best advice - if he's serious and wants to pull the trigger, find an attorney who prefers to use mediation and settlement tactics. Seriously, make sure you have money afterwards to pay for your kids' college educations, not an attorney's kids' college educations.