As others will say, there are options. Rockset helpfully posts links to a bunch of comparisons on their website, and these alternatives include ClickHouse, Elasticsearch, Druid, etc.. https://rockset.com/real-time-analytics-comparison/
I'm inherently biased (as a member of the ClickHouse team). But do check ClickHouse out.
You can always come hang out in our Slack (clickhouse.com/slack) and, of course, the combination of hosted ClickHouse (clickhouse.com/cloud) and the open-source (github.com/clickhouse) may add a bit of comfort when your vendor up and disappears via acquisition.