First off, Welcome to the site!
Secondly, for future reference, no one here will be able to tell you an EOL date for any set. It isn`t public knowledge, and only those who work for Lego higher up in the chain know that info for a fact. We can only speculate based on the market and availability of a set. There seems to be a rumor going around that DS will retire this year, I personally don`t think so. There is no real reason for Lego to do it, unless they release another UCS set. They did recently with the Sandcrawler, but I still don`t see it leaving just yet. End of the year at the very earliest, but I don`t think so.
Tower Bridge is possibly on the way out, and it`s definitely going sooner rather that later, but probably another year. That`s one I`d invest in now if you are interested in doing do, but I`d wait on DS for now. If you wanted to buy into that one, May the 4th or double VIP in April would have been the best times.