I'm in a similar situation. Started as a software engineer this summer and it was a perfect work environment: boot-strapped with fast-growth ($50m in 2 years), pingpong/food, good team, $85-90k + 0.2% equity. Then they hired some executives who started changing our roles and let go some of our teammates. I'm still technically an engineer but I'm working on functional tasks that a high schooler is capable of (eg. powerpoints, researching prices, documenting).

Not sure if I should stay just because it's paying well and is mind-numbingly easy work or leave because it's soul-draining and the company is likely to fail with the new management.