Hi debbie
If you loose your PIP then your partners CA will stop, (there will be a few weeks run on), you will also loose your SDP but this does not automatically trigger a Universal Credit claim.
You may need to claim UC if your income is adversely affected by the losses above, but I would always recommend you seek help from a Welfare Rights Organisation before you make a claim for UC, as once you claim UC you will not be able to go back to legacy benefits.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
