Pablo, I'm going to look at this situation as unbiasedly and as fact-based as possible in my response. The bottom line is, Intel has done nothing of productive use to fix this issue. Sure, there have been a few minor driver updates, followed by even more regressions, along with countless users here giving extremely detailed settings of minor changes they made in an effort to rectify the issue, but this is nothing you can quantify as a fix. I work in IT, and I know what it means to give users answers, support, etc. This is far from that. This card is simply a failure. I'm sorry, it's a failure.
Likewise, Lenovo (and HP that I know of, possibly others) like to dabble in a bit of nonsense known as whitelisting wireless cards. I'm not sure if this is across the board, as I've seen some Lenovos without the whitelist, others with it, but it's worth mentioning. Whitelisting the wireless card means is you cannot change the wireless card. I had a Lenovo with the whitelist and I switched out the trash Broadcom chip that was in it for an Intel. Sure enough it locked on boot and would not go any further. I called Lenovo multiple times to voice complaints, but they fall back on a pathetic excuse, citing "FCC Regulation." Yeah. Yeah that's a lie. Clear as day, a blatant lie. So as a result I was a customer with their product who could not replace a replaceable chip. I say replaceable because you can remove 2 screws, remove the chip, and oh my gosh just like that you swapped it. Brilliant. But with Lenovo putting this checker in the BIOS/POST system, you are effectively locked out on a software level to change it. Your only hope is to find a custom BIOS that has the whitelist removed and flash it. I did this with success, however it's not something I'd want to do on a number of systems. As an example, we have 5,000 systems at work. What if we ran into a monumental issue where the wireless card just needed to be replaced? Or upgraded? At this point you can probably guess that I refuse to touch systems that whitelist their BIOS any longer. Don't worry, once I'm president of the world I'll change this, but until Lenovo changes their foolish behavior I will A) not purchase their systems and B) refuse to be quiet about it. Users must know about this.
So in your case, you're in a serious rock/hard place type of situation. Your BIOS is likely (but not guaranteed, as not all Lenovos do this) whitelist your wireless card. You can try to replace it with another wireless card of similar form factor, but if you get an error on boot, you might be stuck. Couple that with the fact that this card has been out for **over a year** and Intel has yet to effectively DO anything about it, then suddenly I'm not sure what else there is to do on the matter.
Me? I'd try a cheap wireless card of similar form factor. If it works and it's not whitelisted, great, you have a working unit. If it's whitelisted, call Lenovo, and make some serious noise and don't take no for an answer. They sold you this laptop like this. While the wireless issue is Intel's fault, ultimately, Lenovo still put the card in the laptop. They are responsible for providing support for the unit. Can't fix it? Replace it with something that can.
Both Lenovo and Intel have made some outstanding products, and I continue to stand by their products that work and aren't foolishly locked down (i.e. whitelist). That said, it doesn't change my stance on these two particular topics. It's important to understand that I have zero tolerance for the behavior of large companies who take advantage of their customers. Intel refusing to replace this chip for users who have these undeniable "show stopping" problems, along with Lenovo whitelisting their wifi chips, yeah that definitely falls under the category of companies taking advantage of their customers. It's unacceptable, and I refuse to tolerate, hence why I now have a working Dell that is A) Not a 7260 and B) not whitelisted. It works perfectly, and I have zero issues with it.
