For the original scenario, when possible, I deploy a remote scanning server and just make sure the remote scan server can talk to the central. Firewall/Connectivity aside, its super easy to do.
https://www.lansweeper.com/knowledgebase/setting-up-an-installation-with-multiple-scanning-servers/For the cases where that's not possible, and you don't want to go the LSAgent route, you could deploy lspush executable in a login script or something, and have it place the files in a central file share for you to scoop up and import into your LS by simply dropping the files in the import folder on the central server.
https://www.lansweeper.com/knowledgebase/how-to-scan-windows-computers-with-the-lspush-scanning-agen...Regarding the archiving of assets - Lansweeper has an insane amount of asset information (especially for a windows machine) which also includes history (depending on scanned item interval settings) - in order to archive an asset, you would have to make a report or reports, that have all the information you'd ever want to know. A super-report i guess.
Me personally, I keep all assets if possible - i just mark the asset state appropriately (archived/decommissioned/broken/whatever) that way no information is lost, and they fall off of your normal reporting.