God does not expect the impossible of us, and thus if we are unable to hear Mass due to a situation in which no Masses are said nearby or we are impeded from hearing them, we are not guilty of sin for not doing so.
I know some people who were obliged to work in China for several months. As I’m sure you are aware, the authentic Church in China is clandestine. There is a state-controlled church, but that is of course irregular. Moreover, for the safety of the clergy and faithful, foreigners travelling in China are strongly discouraged from attempting to seek out the authentic clergy.
In any case, they visited their parish pastor before departing, and he assigned them alternative devotions, such as praying the hours. If you are seriously considering going abroad to a country where it is impossible to worship, then speak to your parish pastor.
However, there are churches in Sierra Leone, so unless you will be spending a significant amount of time in quarantine, it might not be a relevant point here.