Comment by lephty
Since they invested their time in you, I would suggest that you give back in kind. Call them, send them a note, email/text, etc. It is easier than ever to keep in touch with people now-a-days. Meet them in person if they are open to that and you are able to.
If some of these mentors are retired, I'm sure they would love to hear from a former protege/student/mentee. Watching my dad after his retirement, he always enjoys these interactions with his former colleagues -- talk about their profession or department. Made his day/week in most cases. Retirement can be professionally lonely sometimes.
I've worked directly with several HNW individuals, and the biggest "snub" (real or not) I ever witnessed was a multi-millionaire who sabotaged a mentee's already-disastrous wedding... because he wasn't thanked in the wedding handout.
Dollars meant nothing to him, but control — and meant nothing to this Groom.
>If some of these mentors are retired
Retired people typically rock, so-long as they didn't spend their entire careers being bullies. For several years I lived in a retirement community (as "the help") and the endless dinners/conversations rarely "got old." I mostly enjoyed working with/for elderly retirees, except that most seem to have almost no concept of how much dollars have deflated since their pre-70s/80s/90s gold-backed hayday.
>[things you could do]
Help raise "the next generation" by living well and mentoring your own deserving minds — perhaps have an informal lunch with both your advisor and advisee?