That disease is just as likely to attack heirloom seeds, in fact, more likely. Hybrids are bred to resist the most common diseases like fusarium and verticilium wilt and while hybrids are unpredictable when the seed is saved, you would still get some form of what you planted.
Hybrids are also heavier yielders. If everyone had to plant heirloom seeds we would very soon have famines by the same scenario as the hybrid and GM seeds getting some dread disease.
For the same reason if all farmers were forced to go organic there would be widespread famine.
I too, have my stash of seeds and it contains open pollinated and hybrids.
Ok, but, I can save the seeds of a heirloom plant and replant later. Like you said about hybrids could you save the seeds and replant and get anything? And even if you could, would you get something the next year, or the next? Probably not. With heirlooms you can save the seeds and replant for decades. At least my grandmother did.
I'm not so sure about that. We use to plant nothing but, hybrids, now we use almost all heirloom seeds. Personally, I couldn't tell the difference in the yield.