PC
Thanks to /u/depreciated_ on reddit for their solution:
Run the following script in Powershell (run as Administrator):
New-NetFirewallRule -DisplayName "Destiny2-Solo-1" -Direction Outbound -LocalPort 1935,3097,3478-3480 -Protocol TCP -Action Block
New-NetFirewallRule -DisplayName "Destiny2-Solo-2" -Direction Outbound -LocalPort 1935,3097,3478-3480 -Protocol UDP -Action Block
New-NetFirewallRule -DisplayName "Destiny2-Solo-3" -Direction Inbound -LocalPort 1935,3097,3478-3480 -Protocol TCP -Action Block
New-NetFirewallRule -DisplayName "Destiny2-Solo-4" -Direction Inbound -LocalPort 1935,3097,3478-3480 -Protocol UDP -Action Block
Write-Host "Destiny 2 Solo mode activated. Press ctl + c to deactivate solo mode."
And then run the following when you are done:
Read-Host
Remove-NetFirewallRule -DisplayName "Destiny2-Solo-1"
Remove-NetFirewallRule -DisplayName "Destiny2-Solo-2"
Remove-NetFirewallRule -DisplayName "Destiny2-Solo-3"
Remove-NetFirewallRule -DisplayName "Destiny2-Solo-4"
This will force the game to block specific network ports, preventing other guardians from joining up in your fireteam. Do note as mentioned in his post that the script needs to be run while your ship is fully in orbit, before starting "matchmaking". After a few minutes, the game will automatically start the strike regardless if others join your team (in this case, won't happen), and you'll be free to play any Strikes solo! This applies to both Nightfall strikes, Nightfall: The Ordeal, any strikes in the Vanguard playlists, or Strikes started manually from each planet's map.
PS4
You can set your time back, preferably 1 hour. This prevents others from matching with you, and you can solo strikes this way. Don't forget to switch your system clock back to normal if you want to play with others again.
Your Total Base Power (TBP) is based upon all of your highest Base Power Level equipment, this number will determine the Power Level of items dropped. Legendary (+5) Mods do not count toward your TBP. This will look for all of your highest Base Power Level gear throughout your vault, inventory, and equipped items, feel free to use any equipment you'd like! Furthermore, each slot may be filled with an exotic to count toward your TBP.
Your TBP will be the average sum of all the highest Base Power Level gear. (This number can also be found by logging into Destiny Item Manager.)
Subtract 5 from your TBP to get your Drop Power Level. (Ex: 280 Total Base Power = 275 Drop Power Level)
Drop Power Level Drop / Reward Type
+0 Rare Engrams, Legendary Engrams / Rewards
+3 Crucible Clan Reward
+5 Exotic Engrams
+8 Nightfall Clan Reward
+10 Personal XP Clan Reward
+13 Powerful Gear Milestone Reward
+18 Exotic Quest Reward
+?? Raid Reward
If your Drop Power Level is 275 and you complete a Powerful Gear Milestone you will receive a drop with a Base Power of 288.
These numbers may differ when you reach 285-300 TBP.
Source
Best Answer
Do campaign missions disappear when I complete them?
Yes, the missions will track on the Director until they're all done.
Where are my quests?
In the Quests tab of the main screen, where you find the Map, Destinations, and Store tabs.
How do I replay the campaigns?
If you go to the Tower and visit Amanda Holliday in the Hanger, she has quests which re-start the campaigns for you.