The only forces currently operating STOVL aircraft are the USMC, the RAF/RN (Joint Harrier Force), & the Spanish, Italian, Indian & Thai navies. The Indians plan to replace theirs with CTOL aircraft operating from STOBAR carriers. The Thais have no replacement plans at the moment, & are not thought likely to want F-35B for a long time, if ever. Their mini-carrier is small for the F-35B, & might need a refit, including new lifts.The JSF will be missed if cancelled, i believe mostly the STOVL nations, there are at least half a dozen nations relying on the JSF to provide their STOVL replacement, not least the USMC who are relying on the JSF to replace both Harriers and FA-18's for their fleet, UK, Italy, Spain this alone is approximately 700 aircraft, now dependant on cost which I'll admit I don't know specifics when breaking down airframes, the STOVL JSF may and should go ahead regardless, there is nothing AFAIK even on the public drawing board which represents any replacements of this aircraft type, UCAV in 10 years may be adequate and in Australia's case the final tranche of fighters been listed as possible UCAV purchases but it will not at this time meet the STOVL capability.
That leaves exactly four countries planning or considering the F-35B (note that Spain doesn't have a formal requirement yet). The UK could easily build the CVFs with catapults, & buy CTOL aircraft. That leaves the USMC, Italy & Spain. Spain is building an LHD with a ski-jump, & is considering buying F-35B for it, & currently operates one very light carrier which could operate F-35B, but is a little small. Italy is worst off: Cavour is designed specifically for F-35B, & its cancellation would leave the Italians with an expensive LPH when their Harriers wear out.