No idea what happened to him, he actually looked decent and on the right path before Lombardia.
It is worth mentioning that the operation that he had wasn't the more conservative approach, they implanted a stent into his artery, you're back on your bike quicker, but the risk of things not working out as planned is also higher.
Source:
https://www.sportal.it/ciclismo/l-operazione-di-fabio-aru-divide-i-medici.html
He finished 14th on gc in the last Tour, after coming back from an operation and with an improvised preparation, I think he's not done as a rider.
The bigger problem is that they had him race a gt when he was already cooked for 3 years in a row.
2017: Probably peaks too early (NC and first week of the Tour) and clearly fades at the end of the Tour, somehow still manages to defend his 5th place from an injuried Dan Martin. He's leaving, so Astana send him to the Vuelta right after hit, he fades and cracks on the Angliru stage. They also send him to the Italian Autumn classics, he actually does pretty decent.
2018: New team, nobody but Tiralongo follows him to UAE (shows that he's not easy to deal with). Multiple meltdowns at the Giro and once again he cracks at the end of the Vuelt, the team still sends him to the Italian autumn classics and to Guangxi.
2019: Rushes back after the operation and they send him to the Tour. For no reason he actually tries to ride for gc and holds on to a 14th place on the gc. Then they send him to the Vuelta, not a problem, if he had actually used the Tour as a training race to ride himself into shape instead of hanging on for dear life. Test yourself on a few stages and take it easy on the other ones. I really think that he could have done a good Vuelta, if he did that, top 10 on the gc was possible (the field at the Tour was a lot stronger, the Vuelta had a good top 5, but the 2nd half of the top 10 was pretty shallow).
Of course Aru himself is also to blame, he signed a big contract with Saronni (who has buried many Italian talents, just look at all the great u23 riders who turned pro with him) and wanted to be in charge. I don't really think that Tiralongo being his coach was that muchh of a problem, they both know how he used to train at Astana and what works for him. You can mess up once by trying to mix things up, but I really don't think that Tiralongo was the big problem. It also seems really hard to convince Aru to do something when he isn't 100% behind it, he's really impulsive and a hothead.
So, where does he go from here? Saronni buried him on live TV yesterday (kinda ironic that Saronni of all people talks about someone who faded badly after turning 27...) and I can't see UAE resigning him.
Maybe Savio can save his career, if he's willing to accept a huge paycut (he's pretty much set for life and I always had the impression that Aru's family wasn't exactly poor either). Otherwise a return to Astana could work, if he hasn't burned too many bridges. Otherwise I can't see too many teams going after him, maybe only Israel would actually be willing to overpay him.