The instinct is to try to rescue it until at least 20 seconds have elapsed, after that time only 2 options are employed, option 1 is to fetch a teaspoon and attempt to spoon out the remains.
when that fails it is left with option 2, which is to accept the loss and to continue to drink your tea, unfortunatly most people will drink the rest of the tea with caution, knowing that there is biscuit debris floating near the bottom of the cup, in some extreme cases people have been known to refuse to drink the rest of the tea.