I went to grad school with a guy who was in that situation. He worked at a bank and got laid off during the financial crisis. The plan was for the bank to port

I went to grad school with a guy who was in that situation. He worked at a bank and got laid off during the financial crisis. The plan was for the bank to port the old system over to Java or something like that, and they were "close" to the end of the project and they thought at that point the rewrite team was comfortable enough with COBOL that they could do the rest of the rewrite without him. Turns out that yes they understood COBOL just fine, but they desperately needed his institutional knowledge. He ended up agreeing to come back on a part-time basis at some obscene consulting rate for however long the transition took and in the meantime, he did grad school part-time to skill up.