Game is April 20 at 4:05 vs Houston. First 20k fans get a WS replica ring.
NavyYardNats says that Howie Kendrick will be in attendance. Besides Rainey, Corbin, Parra, Robles, and Doolittle who are still involved with the team, I'd imagine Zimm will be there. Wander Suerro is currently with Houston but is currently with their AAA team.
Looking just at the WS Roster:
Others who are out of baseball and could possibly attend: Strasburg, Anibal Sanchez, Fernando Rodney, Javy Guerra, Matt Adams, Asdrubal Cabrera, Brian Dozier, Kurt Suzuki, and Adam Eaton.
With other teams / still active: Daniel Hudson, Joe Ross, Max Scherzer, Trea Turner, Anthony Rendon, Juan Soto, Michael A. Taylor, Yan Gomes.
2019 playoff players who didn't make the WS Roster: Austin Voth (Seattle), Hunter Strickland (LAA), Roenis Elias (Retired)
Who am I missing?