I think he's the type to leave on a free if he did leave. He's the most well-recognized player playing outside of the US, but he's not the type to put fans in the stands, and his salary would be peanuts compared to what he makes at Everton.
Lando was popular because of his stats and was arguably the best player to ever step on the field for the USA.
I'm not saying Howard wouldn't be welcomed, but I don't think he'd get a DP contract or take a a significant pay decrease either. It's from both a marketing and financial standpoint. I could be wrong though. Personally, I plan on coming to Goodison at some point in my life, but I'm more interested in seeing the likes of Barkley, Lukaku, etc. than Howard.