The poll begs the question - is this about what the DM and DM fiat allows in regards to characters or is it more properly a question of what should happen to your character when someone is playing that character and makes certain decisions that is not consistent with what you feel your character would do?
In the first instance, DM fiat (supported by the rules) has always been in the game. Helms of Opposite Alignment, Belts of Feminine/Masculinity, etc have been ways that the DM can screw with characters and as such, it is 'fair ball'. In some ways, your situation is not too dissimilar from a Helm of Opposite Alignment issue - the character concept gets nerfed and adjustments to the character have to be made. However, that is not what I think your are getting at.
What I think you are getting at is that your character undertook an action you feel that, had you been the one playing your character, that character would have never undertook.
The danger with having others play your character is this - what is considered fair ball and what is foul?
Had your character (while being played by someone else) done something uncharacteristic but the end result benefited you - is that fair or foul ball? If you say 'fair', then having your character suffer a negative consequence for that same action is likewise 'fair'.
If 'foul', then where do you draw the line on what is acceptable for your character? If the party gets into combat and your character does what you would normally have that character do in a combat situation but your character dies..... fair ball or foul? And on it goes.
Bottom line - unless you are willing to accept any and all possible consequences (rewards or otherwise) of having your character being played by another player, you are better off not having your character present or, if you trust the DM, having the DM handle him like as a NPC for the rest of the session.
For our group, we have a 'Bot' rule. Any character whose player is not present becomes a 'Bot' and follows the rules for that Bot. Bot rules are class depend and follow simple 'behaviors' or actions that are typical for that class. Bots cannot do any actions outside of the rules agreed upon for that class.
So, say that the Wizard player is not present. The Wizard-Bot states the wizard remains in the rear and casts spells in support of the party. That means, the wizard-bot is not going to try scout ahead, not going to disarm a trap, not going to close with the enemy, not going to charge a foe to deliver a touch attack, or is not going to sub in on the front line for whatever reason. The bot does not 'orginate plans' nor does the bot 'volunteer' for whatever activity outside of the rules layed out for the bot. Even if the character's player has done such actions with that character previously and such actions are considered 'in character' for that character.
So, if your group had 'Bot' rules, the situation you outlined would not have happened since the dread necromancer bot cannot 'volunteer' or undertake any action what would allow the character to be 'considered' the sacrifice.