After removal or expanders due to Infection do you need to start expander process again or just go to an implant?

Typically a tissue expander is placed following mastectomy for several reasons.  
1. It establishes the breast pocket for the placement of the future implant.  You can think of it almost as a place holder.
2. Over time, tissue expanders further stretch the skin pocket so that the final implant can be placed and look natural.
3. During a mastectomy, the breast tissue is removed.  Sometimes the overlying skin is thin and fragile.  By inserting a deflated tissue expander at the time of surgery, the additional weight or pressure that a larger silicone implant would place on the breast skin is avoided.  Once the tissue has had time to heal and more robust, the implant can be inflated and the expansion process started.
When a tissue expander is removed, the skin tends to contract to a certain degree.  Most patients who needed a tissue expander to begin with will inevitably need it to be replaced if the tissue expander is removed prematurely (i.e. infection).  By putting an implant in outright without first expanding the skin following an infection with skin contraction, the result can be compromised.  Though this is not the case in every situation, it is worth discussing with your treating physician. 

After breast implant loss you typically get shrinkage of the breast skin. In my experience it is most common to need a two stage approach. The first stage to place the expander and stretch up the skin to the volume you desire. The second stage is to place the definitive implant. It is risky to go straight to an implant unless you have soft and pliable skin and only desire an very small breast. If you have any doubt about the advice you have been given I would recommend you seeking a second opinion from an experienced plastic surgeon, all the best.

That is not going to give you the result you area after so it may require another opinion.  Infection in the pocket where an expander has been is a difficult issue.  I typically recommend one more attempt or the reconstruction with your own tissue in the form a DIEP flap, TUG/PAP, or SGAP.