Could my cat be sick or dying?

Sorry for the vague title. On May 29th my two year old cat, Mika, suddenly died. The vet thinks he had a seizure but isn't sure (I'm not actually sure if that's what the vet said. When we brought him to the vet for cremation my mom went inside the building while I stayed in the car with her friend. My mom spoke to the vet but when she tried to tell me what he said I couldn't understand. She's cognitively disabled on top of being a mess because of his death and that made it hard to understand, but I'm pretty sure she said something about a seizure and his heart muscle thickening.).  As far as I know he hasn't had one before and I have no idea what caused it. I wanted to do an autopsy to see if my other cat and dog are at risk but my family doesn't have enough money for one, especially on top of the cremation cost. He would always bite his hocks very badly (We brought him the the vet and she was baffled by it. She needed another vet to take a look and even then they had a hard time figuring out the cause. They diagnosed him with separation anxiety since he had the symptoms and ended up  wrapping his legs up but as soon as it came off he started biting again. They did some other things there but I'm not sure if it's important. If you think it might be feel free to tell me and I describe it to the best of my ability.) and we suspect that might have something to do with it. We also suspect that it might have something to do with genetics. My mom's friend owns his brother and they both generally act... odd and bite themselves (for Mika it was his hocks, while his brother bites the entire back of his legs). My family tends to adopt/rescue instead of buying but Mika was an exception because my mom wanted a savannah after her friend's daughter gave us her savannah but changed her mind and took her back after a few days. We tried contacting the breeder but she died a little while ago.

Now here's my question: Is it possible that my other cat, Gracie, could be sick or dying? Of course my other cats sudden death made me scared that she would die like him but something that happened that made me even more worried. She started cuddling with my mom. I know that doesn't sound bad but she NEVER did that before and I heard that pets tend to act different when they're sick or dying. She usually keeps to herself and doesn't like to give or receive that much affection (except for when she want's to drink from the faucet). Do you think it might be possible that she's like this because Mika died? Is this her way of comforting us and/or comforting herself? It's also worth noting that Mika was an attention hog and was very jealous. It's possible that she might have been afraid to cuddle because of him, but she wasn't cuddly before we got him either. As far as I know she doesn't have any health issues besides a problem with her sinuses that doesn't go away no matter what we do. We're planning on bringing her to the vet soon but I would like to hear what you all think.

If you need to know more about Mika and his death I'm ok with talking about it, just ask. Thank you for any input.

There is no way for anyone here to know whether Gracie is sick and/or could be dying.  Chances are she's fine .

I will tell you that animals definitely feel the loss of their companions, just like people do.  Every time we have lost one of our little furry friends, the remaining ones have become more and more attached to us.  I think they see one disappear and don't want that to happen again, so they get clingy.  Ones who were always standoffish are suddenly lap cats

BTW, my condolences for Mika.  So young to have passed

Very sorry to hear of Mika's passing. May he rest in peace. I think that Gracie senses that everyone is grieving and she probably is as well and she's trying to comfort the hurting. As for Gracie as long as she is eating as usual, pottying as usual and pretty much her normal self besides the extra affection, she should be fine. As for Mika with the heart thickening and the sudden passing it sounds as if he had HCM. Here is a link explaining it in much better detail than I ever could. 

http://www.vetmed.wsu.edu/ClientED/hcm.aspx

I know it doesn't change things but sometimes knowing brings closure. I know that certain breeds including bengals have a higher risk of it. I do believe I lost my first cat due to HCM but like your situation I could not afford a necroscopy. She was a Maine Coon, another breed at higher risk than normal for HCM. It was very sudden. 

Run free Mika.