Actually, I have had the curb side slide deploy partially on the interstate entering Phoenix. It came out at an angle and jammed in place with the forward edge out about ten inches. We were able to limp to a service facility. The issue was a hydraulic line that had worn against a piece of metal until a hole was formed and fluid leaked out. Big mess in the basement, but a bigger problem was avoided. Luckily the extended warranty folks picked up the tab. So, no pressure means nothing keeping the slide in or out depending on which side of the system the failure is in. The same condition could occur, I suppose, if the solenoid relief screws back off. If you have some form of slide lock I suggest you use them.
That said, the straps Winne used to perform that function are often gone along with one of the fittings they attach to. All it takes is forgetting to undo them once. The strap will hold them in against giggling out while on the road, but can not stop them when being powered out hydraulically.
By the way, I had that same slide fail while out. Same reason, just a different line a year later. We were able to power it back in, but it sprayed fluid in the process. We did a Rube Goldberg slide lock and continued to HWH for repair.