Edited: I got a little emotional the first time.
I wouldn't worry too much about Olympus or Pentax going out of business. Spreading rumors and speculations like this is only hastening any damage to the companies. It is not like they are fly-by-night camera companies, you know? They've both been around for many decades. They both make top-quality cameras and optics. They both have a fine selection of optics available.
I would admit that third party lens manufacturers sometimes don't make all their lenses available in Pentax or Olympus mount. But there are enough choices that you can get what you want. The difference being that you may have to pay more for a lens later.
On the other hand, with a Pentax, you can use any Pentax K-bayonet mount lens, auto-aperture type is preferred. Olympus users can buy an adapter to use OM-mount optics on their micro 4/3 cameras. These are manual focus, and available used for very reasonable prices on
ebay.
Take some time to look at Pentax's and Olympus' lens line-up on their website. See if they don't make the lens you need. I bet they do.
It is also worth pointing out that Samsung uses Pentax mount lenses, so you can use Samsung optics too. Olympus micro 4/3 shares a mount with Panasonic, I believe. Are you worried that Samsung and Panasonic are going out of business too?
Bottom line: See which camera you like best. Don't eliminate Pentax and Olympus just because Canon and Nikon are more popular with pros. You are not a pro, and therefore, you do not have all the same priorities. For instance, pros prefer full frame cameras when they buy Canons. So if you're going to buy a crop sensor Canon, (much more affordable) what have you gained over Pentax? Pros carry dozens of pounds of equipment when they go on a shoot. They accept that the best equipment is heavy. (not to mention super-expensive) Is that what you want? Or would you rather have a more compact set-up that still gives image quality that looks just as good as the pro stuff until you zoom into an unrealistic level?
