I'm going to be a little bit of an outlier here.
The advice you're getting from everyone else is probably the right advice. Chances are, it's better to do the "post regularly without graphics" thing in the long run, in order to keep your audience. Because if you post irregularly, your audience will suffer.
You need to decide, first, what the most important thing is for you, personally, to keep the project going. By that I mean: if you believe, fully and completely, that the illustrations are a necessary component to the entire composition, and that what you're trying to create will be incomplete without them, then you need to figure out if the project can survive being incomplete during the time you're working in "degraded mode." Some projects can, some can't. For example, the webcomic "Erfworld" -- Rob Balder (the writer) had long stretches where the artist wasn't available to move the story forward, so he would alternate the comic with prose to make sure there was a more steady stream of content for his audience. His prose turned out to be rather popular, so his "degraded mode" strategy is now officially part of his process.
On the other end is Aaron Diaz, who does Dresden Kodak. He updates once in a blue moon, because the pictures are ready when they're ready. Degraded mode doesn't work for him.
Basically choose the right "degraded mode" and be aware of the results. Choose the one that you know will keep you going. Tactically, in terms of keeping your audience, posts-without-pictures is best choice. But that may not be the choice that keeps YOU motivated to continue, and you may find that the cost of continuing is slowing down your updates and losing parts of your audience.
All that aside, Billy's advice (and everyone else's in this thread) is probably the right way to go. Just be sure it's the thing that'll keep YOU going.