Pretty much how you lay it out. If you are covered by the national agreements there are (from memory) pretty standard processes for removing these and if and how pay protection applies.

If you aren't covered then it will come down to how well the contract is drafted but generally losing the responsibility means in time you lose the benefit.

Depending on what is laid out in your Redundancy & Restructuring Policy and in conjunction with the STPC you should go through the restructure/consultation process over the removal of the SEN point (similar to the removal of a TLR) but it will be safeguarded for 3 years. During the safeguarded period you can still with mutual agreement give the member of staff additional responsibilities appropriate to the value of the safeguarded value.