The context items will remain. By default they are stored in the .node-red folder in a folder called 'context'. However if you delete that folder, all context will be removed.
Case 1 - you have one tab with one flow creating a context variable.
- if you delete the flow and delete the ;context folder' you are all set
Case 2 - you have one tab with two seperate flows and both create seperate context. If you remove flow one and delete the 'context' folder - you will have removed the context variable flow two used along with the one flow one was using.
Case 3 - you have two tabs each with one flow creating seperate context variables. This is the same as case 2 - If you remove the flow from one tab and delete the 'context' folder - you will have removed the context variable from the flow in the secont tab along with the one flow one was using.
You easily can go to the dashboard and select the Context Data
icon

Press the refresh button


then the delete button and remove the variable that way.