The lifespan of a wig depends on the quality of the fibre. Some wigs are made of this really cheap fibre that will frizz and tangle no matter how well you treat them. A well-made synthetic wig, if cared for properly, can be worn hundreds of times without suffering noticeable damage. Usually if you experience a great deal of tangling and have difficulty combing your wig even with a quality wig brush, that means you've got one of those cheap fibre wigs. Not a great deal can be done about that, unfortunately. Normally I'd say that if your wig has started to get frizzy, you should comb it out completely and reset the fibres, but if the fibres are too low quality, you'll just end up ruining your wig. With cheap fibres, the best you can do is get it wet and give it a very low heat treatment. It doesn't get rid of frizz completely, but it does help.
From the description when I bought it, my wig is meant to take heat styling. I have yet to try this and know of at least one occasion when such a claim was made that turned out to be false. I’m not sure what you mean by reset though?
I've heard of a lot of stories where people have melted their 'heat-safe' wigs, but usually upon further investigation you find out that the person did something stupid, like covering their wig in product or taking a four hundred degree flat iron to it, which is not what manufacturers mean when they say it can be heat-styled. The truth is that even most wigs that aren't labelled 'heat-safe' can be styled with low heat. It's just they require such low heat that most hair irons are too hot. The general rule is that if it can burn your skin, it can melt your wig too. Most people style their wigs ['heat-safe' and otherwise] by setting them in pins and rollers and then applying a non-contact heat source like a blow dryer, heat gun, or steamer, but you can use irons if you monitor the heat extremely carefully and use a buffer [like end paper or a heat protection spray] between the iron and the hair. That protection shouldn't be necessary for a heat-safe wig as long as you have your iron on a low setting, but I'd test a few strands before I stuffed a huge chunk of my wig into an iron.
Resetting a wig is a process basically like perming or relaxing for synthetic wigs, except that instead of using perm/relaxing solution, you use steam. It can be used to create a new style in a wig, but you can also use the process to recreate the original style of the wig if the style has been damaged by tangling or mistreatment. Unless your wig has suffered substantial melting or breakage, resetting can make a wig exactly like new. I've gotten wigs that looked like they'd been struck by lightning into pristine, sleek condition using that method.
I recall seeing a tutorial that used leave in conditioner and wetting the wig, then using a comb from bottom to top to get a lot of the tangles out Sadly, I don't think I have the link, but I tried it and it worked for one of my longer wigs
I think the point of using leave in conditioner is to keep from frizzing, like it would with actual hair. Not sure if that would work on all wigs, as they're usually some kind of synthetic material. If all else fails, there's Google to check out what would prevent the frizzing.
So far, no. My wigs are in good shape still. Some minor snags, but no frizzing just yet I don't get many opportunities to wear them, so I usually tie them in sections to keep them from getting tangled in storage