I always say the same about crypts especially. Before my dad gifting/dumped his old tank on me, it was covered in crypts, but they'd been taken over by some nasty black algae that was impossible to remove. He removed every leaf on the plants and stuck some of the roots in a small container outside covered in gravel, then said he wasn't going to bother with them anymore. So I rescued some roots that didn't have any visible algae on them and stuck them in my own tank.
Tough to see in this pic, but the reddish/brownish leaves on the left are some of those plants. Looking at that tank now, and that plant is 2/3rds of the height of the tank, and have groups of them in all tanks since they grew back so lushly and produced loads of baby plants. No algae either, thankfully! Just some root tabs and time, and sprouted back almost immediately, like yours. I always tell people not to give up on crypts now. Amazing plants.