Sadly it's not surprising. He had the toxic infection that almost killed Mike Von Erich (but ruined his brain with an extraordinary fever) but as an old guy and not a more resilient 20 year old.
No Wyatts, no House of Black, no Undertaker, no Paul Bearer, no WCW winning the war for two years which lead to WWE finding their footing, no hardcore becoming the thing to do, wrestling probably wouldn't have evolved into what it is now, an absolute horde of talent wouldn't have the mentoring and success they had, all this and more without Sullivan. A titan of the wrestling business. And at the end, he just loved the beach, the water, and the Red Sox. A good human being.
Very sad news, watched the guest booker with Kevin together Gabe only recently. Also been watching some clips of Kevin in CWF, he had that real believability with his gimmick, I especially liked the angle with Dusty and how he was banned from wrestling from all these different territories for a year but Dream wanted to bring him back. Kevin's sitting there with this sinister grin & rolling his eyes back whilst Gordon Solie is talking. Just great wrestling TV, the subtlety of it in a way, but it's powerful.
Kevin & the Purple Haze are a great pairing too. He also had a great mind for the wrestling business, his guest booker WWF 84 is really interesting.
Like Dusty, he learned from Eddie Graham & it's a shame they all didn't write down what they learned from booking pro-wrestling, as today's bookers would learn so much from them all. WWE should put a best of Kevin Sullivan together of his best promos, segments etc so today's newer fans can learn about him & how he pioneered a lot of todays wrestling in different ways too.