When is the point of no return to get the Baron's unique Gwent card? I've read that his is miss-able if not done in good time. I've already started his quest, and I'm on my way back to Crow's Perch from the pellar after retrieving Princess.
It was missable but the card was patched in. It will be on his table if you didn't play gwent with him back when you had plenty of opportunities. As for where you are in the quest line, you're not quite yet at the point of no return, so to speak as there's no longer a point of no return concerning that card.