You can lose your 10 TAO, if the subnet alpha token goes to zero you cannot exchange it back for 10 TAO anymore.

Think of $TAO as like it is $USDT:

You stake 1 TAO to dTAO subnet token and you get 100 alpha tokens in return.

Alpha token drops 50% in the next weeks, meaning you can only exchange your 100 alpha tokens back for 0.5 TAO losing half of it.