Start a new project in JIRA or whatever. Get rid of the encumbrances of the history of all the accumulated bugs (including some that list mundane "misspellings" of "neighbour").
You mentioned triage. Triage takes place at different levels. Clear the table and focus on the items that will really move your business and the project. The issues that were previously removed - will re-surface if they are relevant to your current customers.
Before you do that, ask - "what IS most important for our business in the next 3/6 months that we can impact with our limited resources"
However, I suspect that if your chart looks that nasty, you'd have a hard time convincing people to do that. In the end, parts of your team could probably now be put to work since they aren't just managing stories in JIRA that will never be completed anymore.
Can't wait for the followup post.