As of August 2020, over 22 million cases of COVID-19 have been reported worldwide, including almost 800,000 deaths. However, the vast majority of COVID-19 cases are not fatal and approximately 15 million people already recovered from the disease. 
Only recently, long-term damages caused by the virus have been identified in patients that are already cured.
A follow-up survey of 25 patients who recovered from SARS-CoV infection during the SARS outbreak in 2002/2003, found that 12 years later 68% had hyperlipidaemia, 44% had cardiovascular system abnormalities and 60% had glucose metabolism disorder.  Given that SARS-CoV-2 has a similar structure to SARS-CoV, similar long-term damage caused by SARS-CoV-2 is likely.
In one study of 179 recovered COVID-19 patients, 87.4% reported that they continuously experienced at least one symptom, especially fatigue or dyspnea, even after the virus could no longer be detected in patient samples. 
A report from Innsbruck University hospital describes severe changes in the lungs of six divers after COVID-19 disease, making it impossible for them to continue their sport. 
Another study of 100 recently recovered COVID-19 patients revealed cardiac involvement in 78% and ongoing myocardial inflammation in 60%, independent of preexisting conditions. 
How exactly the virus causes the long-term damage is still unknown, but long-term damage might also affect patients with mild disease form or even asymptomatic patients.
Most likely, more long-term damage will be observed, as more and more people get infected.
- WHO. Coronavirus disease (COVID-19). Situation Report – 209. Data as received by WHO from national authorities by 10:00 CEST, 16 August 2020. https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200816-covid-19-sitrep-209.pdf?sfvrsn=5dde1ca2_2
- Wu Q, et al. Altered lipid metabolism in recovered SARS patients twelve years after infection. Scientific reports 7.1 (2017): 1-12.
- Carfì A, et al. Persistent symptoms in patients after acute COVID-19. JAMA (2020).
- Hartig F. Tauchen nach COVID-19-Erkrankung. [5th May 2020]. www.wetnotes.eu/tauchen-nach-covid-19-erkrankung/
- Puntmann V, et al. Outcomes of cardiovascular magnetic resonance imaging in patients recently recovered from coronavirus disease 2019 (COVID-19). JAMA cardiology (2020).