I'd probably worry less about wiping your tracks off the internet. It's a futile effort, you'd only be able to remove so much.
Everything you've posted publicly will remain, it'd be practically impossible to prevent specifically investigators from looking at public content you've posted before if there is no option to delete it.
Me personally, I am not going to worry about trying to scrub my presence off the internet. I'm not concerned about whatever investigators can potentially find that I've done publicly.
Like, I cannot have my family know about this forum account and what I've posted right now. But, once I'm dead, if they somehow manage to identify me here after I'm gone, they can read all my posts for all I care. What are they gonna do about it anyway?
That said, I would be concerned about private stuff. Like the login credentials to your internet accounts and stuff on your computer already.
But you can do things to try to prevent your accounts from being broken into if you're concerned.
The first place investigators would most likely start with to get your private data is your physical devices. Those will simply contain all your accounts and lots more right there for the taking when they discover your belongings.
You can prevent this by factory resetting any device you are using now and the ones you've been using in the past before you go.
Better still, change your passwords on your important accounts like your emails and such to something complex and one you haven't used in the past as well.
I think that would make a significant difference (not necessarily 100% though) in obscuring your internet activities if you're worried about investigators/family looking at your stuff. If you did those two things above, they'd have to start from scratch when enumerating your presence online (provided you haven't just used the same username on every platform and such, that would make their job easier).
And, if you used a unique username here and your email account remains secured, they will most likely not discover your SaSu account.