Hi Ann,
Alas, you're right. That particular text inside the widget can't be customized currently. And, you're also right that the next closest thing is to instead show something other than your widget when you're offline. Here is a demo widget-offline image I cooked up for another library recently:
That image could be clickable with a mailto: link or to an email form, of course.
Font size in the widgets can be changed using a simple Wicked CSS Hack, but of course, this won't help in this particular case. But here's how:
Very best,
Pam
LibraryH3lp support