Hold during the downswings.  Maybe even buy some gear if it's selling for cheap.  I've been mining with 50 older GPU's (280x, 290, 290x) and bought my last ones when profitability turned to s**t around 2 years ago.  I thought WTF when I made my last purchase, but have profited nicely since then.  It'll come back, and you just need to be ready for it.