deleting the eVar in your implementation would result in not sending the data to Adobe Analytics. But it would still persist in reporting (eVar2 still holding the old value).
instead of trying to use a default merchandising variable (eVar), I would suggest you have a look at "products". because basically your user is searching for products with some meta data, adding it to a cart and proceed checkout (purchase/use offer).
the merchandising eVars allows you to "stick" variables to a specific product, eg. you can set eVar2 to "abc" for productX and set eVar2 to "DEF" for productY - all on the same call (Analytics track event).
A new clearVars method is available to clear the following values from the instance object like eVars, props, etc... To clear eVar2= Offer1 and to clear the Persisted value use when customer visit Offer 2
The s.clearVars('eVar2') Function