The episode had several threads it was addressing but Gambit clearly had as prominent a role as anyone. Let's recap.
1. He has the nice moment with Nightcrawler.
2. He and Rogue had the airing out of their relationship.
3. He was helping people while Rogue and Mags were unconscious for an undetermined period of time.
4. He also foreshadows his own death when he talks about the Godzilla Sentinel and says if you go at you end up dead.
5. He has the nice action sequence on the motorbike where he flips it and destroys two mini Sentinels with his cards.
6. He also makes a decision crucial to saving the Morlocks as he looks at Rogue fighting mini Sentinels and rather to delay getting to the Morlocks to help her, he correctly judges she can handle.
7. Because of 6 above he arrives just in time to save the Morlocks and shortly after one of them saves the X-men are not their friends.
8. He literally stops a whole freaking train from killing him and the Morlocks with a scarf. A SCARF!!!
9. While Rogue is being emotional, Gambit is cool under pressure. One of the more underrated aspects of this is the fact that throughout this whole sequence when he has every reason to be mad at Rogue and Mags, he remains adult enough to answer Mags questions, take orders from him and give Mags his due when Mags was trying to protect them.
10. After Mags is seemingly killed and Rogue lets her emotions get the best of her with her suicidal attack, (remember Gambit said in 4 above, you go at it you die) Gambit takes one look at his motorbike and makes the split second decision that the only way he can stop a flying Rogue is to charge up and hurl the whole damn bike at her.
11. After this and seeing the Sentinel about to kill Nightcrawler and others Gambit runs headlong into certain death (remember Gambit said in 4 above, you go at it you die).
12. Gambit knows full well he is going to die going at the Sentinel (remember Gambit said in 4 above you go at it you die) and having been observing the Wild Sentinel this whole time including when Rogue and Mags were unconscious almost certainly knows he is too close and fast for the Sentinels retinal blasts to hit him. Due to that observation he likely also knows it has short range attack capabilities and it is my opinion that he knows full well the only option the Sentinel has to stop him is via that stabbing attack. This is Gambits final and greatest gambit. He jumps in the air leaving himself fully exposed to lure the Sentinel into stabbing him. In so doing he knowingly sacrifices himself (remember Gambit said in 4 above you go at it you die) so that he can charge the whole Godzilla Sentinel up and destroy it.
So for me it is Gambit's shining episode. He did what no other mutant could including several Omega level Magneto. It will literally go down as one of the most iconic deaths in superhero media.