
Solidify the "exposure to other platforms"
Try to get it in the contract that they'll cross train you on whatever other technologies they have in house. If the system is truly end-of-life, they won't necessarily see this as making you too mobile. If they *do* offer formal training, try to get it on those other technologies. Good luck, hope the family doesn't mind the move too much.
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Implicitly condoning stupidity since 2001.