Should one say Baruch HaShem L'Olam when davening without a minyan? What if one is davening not in a synagogue but in a home? What if one is davening alone?
Practically speaking, the prayer was instituted for the sake of those coming to synagogue - either "in order to shorten the service... permitting Shmone Esre to be recited safely at home" or "to allow latecomers time to catch up" (Artscroll nusach Sefard). It would seem that logically one davening at home is therefore not obligated to say it. However, my siddur (Tefila Yeshara nusach Sefard) is certainly clear on what is not said by a yachid and it says nothing of the sort here. Furthermore, the Baal Shem Tov was very particular to always say it, and it is known that he would sometimes daven without a minyan.
I recall learning an opinion that one davening at home should not say the final blessing, but perhaps this reflects the opposition some authorities have to the passage altogether. All of this, of course, assumes one holds that it should be said even with a minyan, as some authorities (notably the Baal HaTanya) rule that it represents an unnecessary interruption between the Shema and the Shmone Esre.