Network softwarization is a transformation trend for networks to converge in programmable service platforms able to host different requirements from multiple tenants. The concept of network slicing plays a key role in this trend. It offers isolated logical networks to different tenants over the same underlying infrastructure. Network slices hosting missioncritical services require fast reactions to changes in environment, adapting their capacity as needed to avoid service disruption and performance degradation. This represents a key challenge for the management plane, traditionally under the direct operation of human administrators, unable to provide a nimble enough response rate. To support tenants in driving lifecycle management operations over their network slices in a timely manner, datadriven, closed-loop mechanisms must be designed. In this paper we introduce a solution that takes advantage of events occurring outside the boundaries of a tenant-managed network slice to guide those adaptations. We finally demonstrate the feasibility of the proposal and describe an experimentation scenario to exploit such results.