To be honest, the heart attack has to be taken into account. Even if he's apparently healthy now, he will be getting very regular check-ups for the rest of his career, and there's simply no telling when his doctors might inform him that he has to stop playing then and there. That's the difficulty of signing a player with a serious medical condition. It's the reason he wasn't allowed to play in Italy at all. A player with that kind of health problem is very, very unlikely to get to retire when he wants to.
Don't get me wrong, I love Eriksen. He's been our most exciting player of this generation, and he's so likeable as well. I desperately wanted him at United a few years ago. But if we're signing him now instead of other alternatives, that's really risky with the club in the situation that it's currently in. We can't afford to plan around Eriksen only for him to be forced to retire halfway through next season, leaving us with a void in the squad. Imagine if that happens at the most important moment of the season.
If I felt confident that our other signings don't depend at all on whether or not we get Eriksen, I'd be fine with it. I'm just not convinced that that's the case. I strongly suspect that the club is after Eriksen precisely so that we don't have to spend money on somebody else, and that's worrying. He's not an added bonus on top, he's a transfer target. If we get Eriksen, it means the club won't sign somebody else in his stead, I'm quite certain of that, and that's too big a risk.
Players who have had a heart attack (and he didn't merely suffer a heart attack, he literally died from one and was revived) very rarely go on to play for years afterwards. He has done very well so far since it happened, but there's a very real chance that his doctors will one day tell him that he has to quit immediately. Even if he's a free transfer, that kind of instability is not what the club needs right now. The next couple of seasons may be the most important in this club's history.