Periodic balancer chain slack/tension adjustment (merely loosening and then tightening an externally-accessible bolt head) remains sound maintenance.
The doohickey (idler shaft lever) was upgraded with the release of the 2008 model KLR650s. While previous models of this component sometimes failed with catastrophic collateral damage, I'm unaware of any subsequent doohickey component failure, although spring tension issues have surfaced.
All this said: It's not a lead-pipe cinch certainty any KLR650 of any vintage will turn into a pumpkin at midnight if the doohickey is not upgraded. With worldwide production over more than 25 years, how many KLR650s now in operation, percentage-wise, have aftermarket doohickeys? (Rhetorical question.)
An aftermarket doohickey, and particularly a "torsion spring," enhance probabilistic reliability and durability. Whether these upgrades exist as mandatory, essential modifications for all model years remains uncertain, IMHO. I think somewhere (Perhaps "west of Laramie" as in the classic Jordan Playboy automobile advertisement), at least one KLR650 rider exists who never heard of the doohickey, or the Internet, riding along peacefully to the end of his motorcycle's service life; YMMV!