A lot of gods died long before the Spellplague during the Time of Troubles (the events that led up to BG1 and 2). Bhaal was killed. Mystra was killed and passed his mantle on to Midnight. Cyric killed a whole bunch of gods and took their portfolios, many of which then got taken back off him and shared out (Myrkul's got handed off to Kelemvor, for example). Lolth escaped the Time of Troubles by killing herself, but instead of having kids with mortals like Bhaal did she just had lots of spiderlings who she kept in her nest the whole time until one of them emerged the survivor and became the new Lolth.
Every one of those gods you mentioned are already back. They came back in the Second Sundering. It was basically WotC fix for all the unpopular changes they made in 4e.
