I'd say it's probably fine for now, keep an eye on the paintwork to see if there is any fracturing going on. Long term you probably want to get the seatstay replaced. A competent framebuilder will be able to do this for you no problem, although you will need to budget for repainting as well.
Coincidentally I've been looking at getting a steel frame repaired recently as I've got a Pug I need fixing, it will likely cost in the region of £150 to replace the stay, although you'll need to speak to the workshop. Budget a little more for shipping and repainting to be safe.