If dealer support is important to you, then I'd shop dealers, not just tractors. What do I mean? I don't think LS Tractors are going away anytime soon. LG is LS, or rather thats how it started. But most dealerships are typically small 'mom and pop shops' that sell all makes and models. My local LS dealership sells Giant, Solis, TYM, and a slew of other manufactures for lawn mowers and chainsaws. They used to sell Mahindra, but dropped them a few years ago now. My little dealership, while it is growing and has been wonderful to work with, might close its doors or drop LS like they did Mahindra. However, knowing that my two local New Holland dealerships sell all the parts for my tractor, I'm not too worried. Thats not to say though that the big dealership chains wont move or close down. The JD dealership in my small home town, that was always on the edge of town, in the center of a MAJOR farming community, closed it doors and move two hours away.
I suspect the NH dealerships wouldn't work on my LS tractor either. But I can get parts there. Since I do all my own maintenance, I don't relay on the dealership for repairs. HOWEVER, I have not had an issue with the computer *yet* (knock on wood), but IF I did, then I know my local LS dealership would take care of me. But if they closed down or stopped supporting LS, then I'd need to trailer my LS a few hours to the next dealership. And again, I'd find it very hard to believe that LS would simply stop existing all together.
Dealers aside, I do not regret my decision to purchase my LS tractor. I use it and abuse it just as much as any Kubota or JD owner. If you take care of it, you probably wont have serious issues.
If the Yanmar is so much more expensive for the same size tractor with similar options, imagine what the price difference would be for the same parts. Either way, its your money and your decision.