Driving with a solid check engine light

The solid check engine light in my 2008 Tundra
came on. Took it to the dealership and they say it's
caused by a leak from my rollover valve. I was told
driving it with the light on causes the truck to go
into a "safe" making the engine run lean and
possibly doing more damage later.

I called a local repair place that specializes in
Toyotas and told them what the dealership found
out and their suggestion not to drive it. He said he
thought it was a scare tactic and that if he was
me he would go on the trip I plan on taking to
another state and have it fixed when I get back.

Who's right? Is there any potential problem from
taking a trip with the light on or no?