Can you decay out of a league
EXample silver V ----> Bronze 1
by decay I mean keep losing on 0 lp
EXample silver V ----> Bronze 1
by decay I mean keep losing on 0 lp
You can decay out of your tier, but only from Plat and above; Gold and below do not experience decay for inactivity.
If you mean can you get demoted for losing games, yes you can. At 0 LP (or below if you dodged some games at 0) losing games can result in dropping to the next tier, but your MMR must be very low for your division for this to happen.
You can get more information on demotion and decay in Ranked Play here; https://support.riotgames.com/hc/en-us/articles/204010760-Ranked-Play-FAQ#h3
Only for Plat and above. Gold and below are safe from Decay.