Good question. Like many others, POTF2 and the Episode I lines are what got me back into collecting in the first place, so if they never existed, I kind of doubt I'd be collecting too much of anything. However, I always did have my vintage figures from my childhood, and there's a chance that I would be working towards a complete collection of that. On a related note, if just "modern" Star Wars was done or didn't exist, I'd likely devote that collecting time and money to the vintage line, first completing the figures and then working on vehicles/playsets and/or a small carded collection.
If there were no Star Wars at all, I'm guessing we'd just have more in savings, or upgrades on other things (house updates, car, television, computer). I basically just use "extra" income to fund my collecting, and I don't put it ahead of bills or "needs", so I'd likely just funnel it into savings or elsewhere. If I continued collecting anything (non-SW), it would likely be the Marvel Legends line and comics, both of which I buy some of now, but I'd probably expand a little bit further. Oh, and definitely more DVDs. I pretty much buy the ones I really want now when they come out, but others I kind of space out or ask for as gifts. I could see the collection expanding a fair amount if I had that extra money to put towards it.