In the picture I attached is the example screen for how setting up a guided game will work in destiny 2. But you will notice that the heroic difficulty option does not have this feature. While I know this is by know means confirmation that heroic endgame content will be off-limits for solo players, this does raise concerns on whether there still will be content that you need a pre-assembled group for. As a solo player, im really hoping this is not the case.