You have to find out why the knockdown of a gene produces cellular death. I mean the mechanics involved in the death mechanism. What pathways are affected by the ablation, which genes participate, etc. Once you know this you will probably be able to discover if there is some irreversible step that impedes rescue.
Some lncRNAs work in cis and as a result expressing them from an exogenous plasmid, or even from stable integration in a different chromosomal locus will no work.