If you really want people to stay, might as well make the milestones based on time participated in the guild 
I like this idea, the upgrades resetting is a must.
But is this really necessary? These bonuses can't really be to effective, otherwise you run the risk of people never joining lower guilds since they could easily go inactive and the player will be forced to loose all their milestones.
(since nobody wants to stay in an guild that could go inactive)
- Don't think it'd change much as far as 'hopping' goes.
I like this idea, the upgrades resetting is a must.
But is this really necessary? These bonuses can't really be to effective, otherwise you run the risk of people never joining lower guilds since they could easily go inactive and the player will be forced to loose all their milestones.
(since nobody wants to stay in an guild that could go inactive)
- Don't think it'd change much as far as 'hopping' goes.