Absolutely. Those stick-ons are great for measuring the temperature of the fermenting wort, but you will need a thermometer for all sorts of other things in brewing: rehydrating yeast (as you now know), steeping grains, cooling wort, and maybe someday your own mashes ... so you will want to get at least one thermometer. I have a couple of simple probe thermometers, and I keep one on hand at all times when I'm doing anything relating to brewing.
The reason your OG was so low when you measured is probably due to mixing. It's very hard to mix extract and water all the way, and so it's very common for extract brew samples to give inaccurate OG readings. But that's not necessarily something to worry about. With extract brews, you should hit the recipe OG right on if you followed the instructions.
What was the recipe OG supposed to be? If higher than 1.041, then the fact that you're at 1.041 now means you probably do have some fermentation going, regardless of the lack of activity in your airlock.
But yes, if the recipe OG was 1.041 and you're still there, your yeast are probably dead in the water (so to speak
). If you can wait a day or so and take another gravity reading, do so. And if the gravity hasn't moved by then, you will need to repitch.
