The death of that fissure might be a short intermission rather than the end. We could see a new fissure opening very soon. See the latest update from the Met Office:
"According to GPS and satellite-based measurements, ground uplift in the Svartsengi region was apparent immediately after the eruption began on the evening of 18 December. Initial measurements show that the rate of uplift is greater than before the eruption occurred. This signifies that magma accumulation continues unabated beneath Svartsengi. This development will likely lead to another dike intrusion and, ultimately, a volcanic eruption. In the event of an eruption, the most likely source region is between Stóra-Skógfell and Hagafell.
Continuous GPS measurements show that the rate of daily ground uplift at Svartsengi between 10 November, when the magmatic intrusion formed, and 18 December progressively declined. This process is likely to repeat itself, meaning that the next dike intrusion could begin with little warning when the uplift rate decreases again. Therefore, the likelihood of an eruption increases day-by-day."
https://en.vedur.is/about-imo/news/a-seismic-swarm-started-north-of-grindavik-last-night