Put the pack back in the fridge and buy more yeast.
Put the pack back in the fridge, order a starter kit, make a starter and brew.
Brew a smaller batch… maybe 2 gallons or so. Then rinse the yeast and save it for another larger batch later.
Brew something else that’s a lower gravity. First thing that comes to mind, Patersbier. Simple grain bill, 1 hop, and the yeast from the Tripel should work just fine for a Patersbier. Then rinse and collect the yeast from the Patersbier and you’ll have enough to brew your Tripel in just a few weeks.
Make a 2L starter in a 1gal glass jug (apple juice comes in these at the store). Use some of the extract from the tripel kit, ferment the starter at a modest temp and pitch the whole thing wort and all into the batch so you don’t lose any gravity on the kit itself.
That said, a smacked pack that went back in the fridge will still have plenty of viable yeast for weeks, enough for a starter for sure.
I think the nutrient pack you break open only has a very little bit of sugar to cause enough swelling that you know the yeast is alive. It won’t break open and the yeast don’t all die just because they’ve had a tiny snack.