Bob, there's nothing 100% safe for the future, Google is a private entity and they make the rules of their own game. However you can 99% sure that links will always be in their algo, just because is the inner nature of the www to have sites interlinked. I imagine that they'll become every day smarter in detecting patterns and automated links or human trying to manipulate the algo, but what they won't never control is human manual editing. It has no (huge) patterns and it's natural which is what they really want.
About your alumnis I don't have the compelte view of your market and situation but if I understand yyour position: they know that they're helping you but you're not giving nothing back to them. I think that since they've studied in your center they've been selected as top alumnis and been given a badge to demonstrate that. If I were them I would like to show it, so ask them to write a post, I think that the value for them here is intangible, jsut ego-boosting you need to play in that ground, I don't know how renowned you are in your market but someone is always happy to be endorsed by a structure (maybe you can offer special linkedin endorsemnent for a really short group with good websites
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