No. It means that we need to use 10,000 as a unit of counting. You would not do that if only 10,00 were dying. You'd use this expression if you don't know the exact number but think it's somewhere in the range 20,000-190,00 or even more.
If over 200,000 to over a million were dying, you'd use the phrase hundreds of thousands.
I think it would be more typical to switch to "nearly 100,000" or "over 100,000" once you hit the 100,000 mark. To me, tens of thousands means somewhere between 20,000 and 90,000 but more likely under 50,000.
These terms are often used when no one knows the exact count but they know that it is at least the minimum indicated by the phrase.