Is switching from Traditional Silver Annual Service Plan to Cloud Based mandatory?

We are a small General Contractor that has run Sage 300 CRE from a single Windows PC in our office for more than 20 years.  We have no workstations.
We do not wish to have timecards or Invoices entered into our system remotely.   We use the basic Modules:  A/P, P/R, J/C, G/L, F/S and C/M.  We do not use it for Estimating, Crystal Reports or Project Management.
We are having several 3rd party Vendors telling us we need to migrate to the cloud.  That Sage is going Cloud based only and we need to purchase new software from them.
Is this true?   
I wish to not make any changes and still pay annually for our Service Plan.  Will that be possible for the future?