I always feel weird commenting on health issues without the full picture, but I would not be surprised if he could play again.
I do not at all think that his condition will cause sudden death on the court, unlike the problems with Hypertrophic Cardiomyopathy, which I believe is what Reggie Lewis had, and unlike the potential of a ruptured aortic aneurysm or ruptured dilated aorta, which I think if memory serves correctly, is what Chris Wilcox, Etan Thomas, and Jeff Green all had surgeries to fix/prevent.
Bosh has blood clots that form in his veins. This can be for a few reasons, mostly either he has a genetic predisposition toward forming clots or he has bad luck. Being physically active decreases blood clots, but long periods of not moving (the classic scenario being an airplane ride, which NBA players have a lot of) increases the risk; blood will pool in the veins of his legs; if it hangs around too long it will start to clot; the clot will continue to grow. This is why it seemed like a "calf strain" then chest pain.
The danger of the clots is that they can become dislodged and get stuck the next time it hits a smaller blood vessel; if you follow the chart of the cardiovascular system, the vessels get bigger as they get closer to the heart, then smaller again, so a dislodged venous blood clot tends to get stuck in the lung. If it is a small clot, it can cause pain, sometimes kill some lung tissue off, which can get infected, etc. The major danger is if a large clot gets stuck in the main pulmonary artery, you basically get a full traffic jam of blood and no blood can move forward anywhere, and you can die. Very scary, but those size clots don't happen in the flow of a basketball game; they take time to grow. Such a clot typically has to be the size of your thigh vein; the veins in the calf and arm are extremely unlikely to be life threatening.
Now, the treatment for someone who is prone to clots is using "blood thinners," which typically require a lot of frequent monitoring to make sure he is taking enough but not too much medicine. Generally, the amount needed is nowhere close to the amount that would cause dangerous bleeding, and I am sure that Bosh would get good, frequent medical care from a team investing in him.
So I am surprised that no doctor would clear him either to play on a standard preventive dose of blood thinners or, knowing his history, would develop some plan to not let him stay completely still on plane rides and use an ultrasound to check his veins frequently for early clots. Either way, I don't think he is at all likely to drop on the court.