We run our evaporator on normal years to support our maple festival which is on March weekends (not this year!). As a result we're usually always doing short runs mid week only if required so that we can ensure running on weekend. We've often left for two or three days with no issues. As Dave said, sugar content keeps evap pan from freezing very hard if at all. Two issues we have had: Intake float box freezes fairly solid - does not damage the float box but makes it hairy on startup as the evaporator is starved until it eventually thaws! The finishing pan is also not an issue. On next start up we just bring the firebox back up and we start producing syrup an hour or two after fire up. We have had ,on several occasions, a small bit of scale cause the finishing pan float valve to get stuck open and thus flood which is pain in the neck. We sometimes close the valve between the two pans but need to be sure latent heat in the firebox cant boil the finishing pan dry.
Our bigger issue is shutting down in warmer weather where microbial growth can spoil the sap in the evaporating pan.