Return row for GROUP BY CASE WHEN IS NULL THEN (...) ELSE (...) even if record does not exist - sql

Question

Let's consider the following scenario.
CREATE TABLE Replicant (Name NVARCHAR(10),Gen INT);
INSERT INTO Replicant VALUES ('tymtam', 2), ('Roy', 6);
SELECT
CASE WHEN Gen < 10 THEN '<10' ELSE '>=10' END as 'Gen',
count(*) as 'Count'
FROM Replicant
GROUP BY CASE WHEN Gen < 10 THEN '<10' ELSE '>=10' END;
The result is a single row:
Gen Count
<10 2
Can I up-sophisticate the query so that I get a zero for the ELSE case?
Gen Count
<10 2
>=10 0
Update 2
My discriminator is 'is null'
SELECT CASE WHEN Gen IS NOT NULL THEN 'Known' ELSE 'Unknown' END as 'Gen', count(*) as 'Count' FROM Replicant
GROUP BY CASE WHEN Gen IS NOT NULL THEN 'Known' ELSE 'Unknown' END;
The result is
Gen Count
Known 2
and I yearn for
Gen Count
Known 2
Unknown 0
Update 1
My context is that I have pairs of queries (metrics) for different generations of replicants:
INSERT INTO [dbo].[Metrics] (...) SELECT
'Metric X for >=10' as 'Name',
COUNT(*) AS 'Count',
(80_char_expression) AS 'Sum',
(80_char_expression) AS 'Min',
(80_char_expression) AS 'Max',
0 AS 'StandardDeviation'
FROM Replicant
WHERE TimestampUtc > DATEADD(WEEK, -1, Current_Timestamp)
AND Gen >= 10
INSERT INTO [dbo].[Metrics] (...) SELECT
'Metric X for <10' as 'Name',
--7 lines repeated from the 1st query
AND Gen < 10
I would prefer to have a single select to insert two rows, even if there are no records.

Answer 1

You can try to use UNOIN ALL make a comparison table for your score then do outer join
Query 1:
SELECT t1.word,
COUNT(Name) 'Count'
FROM
(
SELECT '<10' word,9 maxval,0 minval
UNION ALL
SELECT '>=10' word,2147483646 maxval,10 minval
) t1 LEFT JOIN Replicant on Gen BETWEEN t1.minval AND t1.maxval
GROUP BY t1.word
Results:
| word | Count |
|------|-------|
| <10 | 2 |
| >=10 | 0 |

Answer 2

You can use left join:
SELECT v.Gen, COUNT(r.gen) as cnt
FROM (VALUES (NULL, 10, '<10'),
(10, NULL, '>=10')
) v(lo, hi, gen) LEFT JOIN
Replicant r
ON (r.gen >= v.lo OR v.lo IS NULL) AND
(r.gen < v.hi OR v.hi IS NULL)
GROUP BY v.gen;
You can also use conditional aggregation and unpivoting:
select v.*
from (select sum(case when r.gen < 10 then 1 else 0 end) as gen_1,
sum(case when r.gen >= 10 then 1 else 0 end) as gen_2
from replicant r
) r cross apply
(values (gen_1, '<10'), (gen_2, '>=10')
) v(cnt, gen);