Q:

What are the parameters for washing after excusing one's self in the middle of the meal?

If I recall correctly from Chayei Adam and elsewhere, if you're in the middle of a bread-based meal and excuse yourself to defecate, first of all you should wash with soap and water for hygienic purposes, as you always should after using the restroom! But after that,   you do a ritual washing and make "al netilas yadayim" as you usually would when starting to eat bread. 
This halacha is the subject of some discussion, and not agreed-upon by everyone.
According to those who do require washing, however, what are the parameters of this washing?  Can I talk afterwards?  Do I say a new hamotzee if I'm having more bread?  What if I wasn't in the mood for more bread, just cake?  Just meat?  Just water?

A:

As you probably know, whether you make a bracha after going to the bathroom could be a mi.yodeya question in its own right.
The basis for not talking after netilas yadayim is "teikef l'netilah seudah".  Since you are already involved in the seudah, there is no issue.  (The eating of bread merely signifies the beginning of the seudah.)
Your bracha rishona on the bread is not affected by going to the bathroom per se.  The only thing that will affect your bracha rishona on bread is hesech daas (see S.A. O.C. 178-179) which is not an issue when just going to the bathroom.
The takanah for netilas yadayim is only for bread.  A similar halacha would be if someone made a mezonos on a doughnut and, after finishing, decided to have another.  Although he may have to bench afterward on what he already ate, he would not recite hamotzi unless he was now going to have an appropriate shiur.

A:

According to Rabbi Yosef Gavriel Bechhofer, if you want to eat more bread, you should wash, say al netilat yadayim and then not talk until you say hamotzee. 
If you don't want to eat more bread, you don't have to wash.

