Maybe...maybe not. Depends on how flexible you can be. If you have a specific list of places and times you want I'd say you're probably going to be disappointed. But if you have a list of places you're willing to try, and will be happy to just get in at whatever time you can take, chances are you'll find places to eat.
I've had situations in the past where I've booked ADR's just three weeks before. Did I get a prime time? No...but I still got in.
Just this past spring my daughter was at WDW with her senior class and they wanted to eat at a TS somewhere. They weren't very picky, and the concierge at their hotel had NO trouble finding them a place to eat.
If you're excited about a spur-of-the-moment trip, then you're probably the type who can be excited about dining-on-the-fly...meaning just take what you can get as long as you have a place to eat.