I used to specialize in migrating applications from their native RPG / COBOL to C so they could run on Linux or Windows. There aren't many of us under 35 with experience in COBOL / RPG but I have 0 desire to maintain COBOL/RPG apps, they'd have to throw an ungodly amount of money at me to make me even consider it. I know of many, many large Fortune500 companies and government entities who are still running on AS/400s and System/36's, most of whom are reaching "critical mass" so to speak. I always say to start rewriting the applications ASAP in their preferred language because migrating will likely cost a similar amount (it is INCREDIBLY labor intensive) and will not provide you with human-readable C code.