Can a negotiator stop while negotiating a deal? Would this cause a loss?

It depends.

For example:

No, if you are about to close the deal. I would recommend you do not stop.

Yes, if it is a tactic, to recup and align with your team and add some pressure to the other side.

Yes, one can stop negotiating a deal without any loss for different reasons.

Negotiator has to set the ranges during which he has to continue negotiation and set a target to achieve his goals. If he does not reach to his set target he may quit to avoid a loss.

If a negotiator stops negotiating temporarily as a Delay Tactics just to give PAUSE to that negotiation session to build pressure on other party then again it's not a loss. This pause of negotiation should be applied after pushing the opponent party into uncomfortable zone by using many other negotiation tactics like "Artificial Deadline Pressure Tactics" etc. and by throwing ball into his court.

no , the negiotaitor must keep the door open for next session ,as many changes may happened

It is hard to answer, because the answer depends on many factors like time, cost, alternatives, target.....etc

Zain, yes a negotiator can stop during negotiations. It can be a tactical use of time eg time out for a coffee or a more strategic use of time in order to gather more information or other resources. As negotitations are progressing you are becoming more aware of the other persons interest and information. Stopping can definitely be a useful tactic in the negotiation process. Whether this causes a loss or not at the time i would say no, like our colleagues have said the loss will only be realised at the conclusion of the negotiations. 

No ... Definitely their will be no loss until the deal is made / complete 

It depends on the stage of negotiation, and the kind of negotiation

If you Planned well for stopping, It will be no or minimum loss

Well it completely depends on the stage of negotiation or discussion.

The Negotiatior do takes time, just to have a firther reference check or to dig more details on the profile, or to compare the Profile with another and see what suits best.

No if it was well planned and based on knowledge .

a true negotiator (with high communication skills ) knows when to stop , sometimes stopping may increase the winning ratio of the deal based on many factors like time .

Stopping to negotiate is also a kind of negotiation. Used in extreme cases to send signal to other party that now there is nothing left on the plate, in a way it is asking for a decision.